(Slip Opinion) OCTOBER TERM, 2011 1 

Syllabus 

NOTE: Where it is feasible, a syllabus (headnote) will be released, as is

being done in connection with this case, at the time the opinion is issued.

The syllabus constitutes no part of the opinion of the Court but has been

prepared by the Reporter of Decisions for the convenience of the reader. 

See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337. 

SUPREME COURT OF THE UNITED STATES 

Syllabus 

ARIZONA ET AL. v. UNITED STATES 

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR 

THE NINTH CIRCUIT 

No. 11–182. Argued April 25, 2012—Decided June 25, 2012 

An Arizona statute known as S. B. 1070 was enacted in 2010 to address 

pressing issues related to the large number of unlawful aliens in the 

State. The United States sought to enjoin the law as preempted. The 

District Court issued a preliminary injunction preventing four of its 

provisions from taking effect. Section 3 makes failure to comply with 

federal alien-registration requirements a state misdemeanor; §5(C)

makes it a misdemeanor for an unauthorized alien to seek or engage 

in work in the State; §6 authorizes state and local officers to arrest 

without a warrant a person “the officer has probable cause to believe 

. . . has committed any public offense that makes the person removable from the United States”; and §2(B) requires officers conducting a 

stop, detention, or arrest to make efforts, in some circumstances, to

verify the person’s immigration status with the Federal Government. 

The Ninth Circuit affirmed, agreeing that the United States had established a likelihood of success on its preemption claims. 

Held: 

1. The Federal Government’s broad, undoubted power over immigration and alien status rests, in part, on its constitutional power to

“establish an uniform Rule of Naturalization,” Art. I, §8, cl. 4, and on

its inherent sovereign power to control and conduct foreign relations, 

see Toll v. Moreno, 458 U. S. 1, 10. Federal governance is extensive 

and complex. Among other things, federal law specifies categories of

aliens who are ineligible to be admitted to the United States, 8

U. S. C. §1182; requires aliens to register with the Federal Government and to carry proof of status, §§1304(e), 1306(a); imposes sanctions on employers who hire unauthorized workers, §1324a; and specifies which aliens may be removed and the procedures for doing so, 

see §1227. Removal is a civil matter, and one of its principal features 
 

 

 

 

2 ARIZONA v. UNITED STATES 

Syllabus 

is the broad discretion exercised by immigration officials, who must 

decide whether to pursue removal at all. Immigration and Customs 

Enforcement (ICE), an agency within the Department of Homeland 

Security, is responsible for identifying, apprehending, and removing 

illegal aliens. It also operates the Law Enforcement Support Center,

which provides immigration status information to federal, state, and

local officials around the clock. Pp. 2–7.

2. The Supremacy Clause gives Congress the power to preempt 

state law. A statute may contain an express preemption provision, 

see, e.g., Chamber of Commerce of United States of America v. Whiting, 563 U. S. ___, ___, but state law must also give way to federal 

law in at least two other circumstances. First, States are precluded 

from regulating conduct in a field that Congress has determined

must be regulated by its exclusive governance. See Gade v. National 

Solid Wastes Management Assn., 505 U. S. 88, 115. Intent can be inferred from a framework of regulation “so pervasive . . . that Congress left no room for the States to supplement it” or where a “federal

interest is so dominant that the federal system will be assumed to

preclude enforcement of state laws on the same subject.” Rice v. Santa Fe Elevator Corp., 331 U. S. 218, 230. Second, state laws are 

preempted when they conflict with federal law, including when they

stand “as an obstacle to the accomplishment and execution of the full 

purposes and objectives of Congress.” Hines v. Davidowitz, 312 U. S. 

52, 67. Pp. 7–8.

3. Sections 3, 5(C), and 6 of S. B. 1070 are preempted by federal 

law. Pp. 8–19.

(a) Section 3 intrudes on the field of alien registration, a field in

which Congress has left no room for States to regulate. In Hines, a 

state alien-registration program was struck down on the ground that 

Congress intended its “complete” federal registration plan to be a 

“single integrated and all-embracing system.” 312 U. S., at 74. That 

scheme did not allow the States to “curtail or complement” federal

law or “enforce additional or auxiliary regulations.” Id., at 66–67. 

The federal registration framework remains comprehensive. Because 

Congress has occupied the field, even complementary state regulation

is impermissible. Pp. 8–11.

(b) Section 5(C)’s criminal penalty stands as an obstacle to the 

federal regulatory system. The Immigration Reform and Control Act 

of 1986 (IRCA), a comprehensive framework for “combating the employment of illegal aliens,” Hoffman Plastic Compounds, Inc. v. 

NLRB, 535 U. S. 137, 147, makes it illegal for employers to knowingly hire, recruit, refer, or continue to employ unauthorized workers, 8

U. S. C. §§1324a(a)(1)(A), (a)(2), and requires employers to verify prospective employees’ employment authorization status, 
 

 

 

Cite as: 567 U. S. ____ (2012) 3 

Syllabus 

§§1324a(a)(1)(B), (b). It imposes criminal and civil penalties on employers, §§1324a(e)(4), (f), but only civil penalties on aliens who seek, 

or engage in, unauthorized employment, e.g., §§1255(c)(2), (c)(8).

IRCA’s express preemption provision, though silent about whether 

additional penalties may be imposed against employees, “does not bar 

the ordinary working of conflict pre-emption principles” or impose a 

“special burden” making it more difficult to establish the preemption

of laws falling outside the clause. Geier v. American Honda Motor 

Co., 529 U. S. 861, 869–872. The correct instruction to draw from the 

text, structure, and history of IRCA is that Congress decided it would 

be inappropriate to impose criminal penalties on unauthorized employees. It follows that a state law to the contrary is an obstacle to

the regulatory system Congress chose. Pp. 12–15. 

(c) By authorizing state and local officers to make warrantless 

arrests of certain aliens suspected of being removable, §6 too creates

an obstacle to federal law. As a general rule, it is not a crime for a

removable alien to remain in the United States. The federal scheme 

instructs when it is appropriate to arrest an alien during the removal 

process. The Attorney General in some circumstances will issue a

warrant for trained federal immigration officers to execute. If no federal warrant has been issued, these officers have more limited authority. They may arrest an alien for being “in the United States in

violation of any [immigration] law or regulation,” for example, but only where the alien “is likely to escape before a warrant can be obtained.” §1357(a)(2). Section 6 attempts to provide state officers with 

even greater arrest authority, which they could exercise with no instruction from the Federal Government. This is not the system Congress created. Federal law specifies limited circumstances in which 

state officers may perform an immigration officer’s functions. This 

includes instances where the Attorney General has granted that authority in a formal agreement with a state or local government. See, 

e.g., §1357(g)(1). Although federal law permits state officers to “cooperate with the Attorney General in the identification, apprehension, 

detention, or removal of aliens not lawfully present in the United

States,” §1357(g)(10)(B), this does not encompass the unilateral decision to detain authorized by §6. Pp. 15–19.

4. It was improper to enjoin §2(B) before the state courts had an

opportunity to construe it and without some showing that §2(B)’s enforcement in fact conflicts with federal immigration law and its objectives. Pp. 19–24.

(a) The state provision has three limitations: A detainee is presumed not to be an illegal alien if he or she provides a valid Arizona

driver’s license or similar identification; officers may not consider 

race, color, or national origin “except to the extent permitted by the 
 

 

 

 

4 ARIZONA v. UNITED STATES 

Syllabus 

United States [and] Arizona Constitution[s]”; and §2(B) must be “implemented in a manner consistent with federal law regulating immigration, protecting the civil rights of all persons and respecting the 

privileges and immunities of United States citizens.” P. 20. 

(b) This Court finds unpersuasive the argument that, even with 

those limits, §2(B) must be held preempted at this stage. Pp. 20–24.

(1) The mandatory nature of the status checks does not interfere with the federal immigration scheme. Consultation between federal and state officials is an important feature of the immigration 

system. In fact, Congress has encouraged the sharing of information

about possible immigration violations. See §§1357(g)(10)(A), 1373(c). 

The federal scheme thus leaves room for a policy requiring state officials to contact ICE as a routine matter. Cf. Whiting, 563 U. S., at 

___. Pp. 20–21.

(2) It is not clear at this stage and on this record that §2(B), in 

practice, will require state officers to delay the release of detainees

for no reason other than to verify their immigration status. This 

would raise constitutional concerns. And it would disrupt the federal 

framework to put state officers in the position of holding aliens in

custody for possible unlawful presence without federal direction and 

supervision. But §2(B) could be read to avoid these concerns. If the 

law only requires state officers to conduct a status check during the 

course of an authorized, lawful detention or after a detainee has been 

released, the provision would likely survive preemption—at least absent some showing that it has other consequences that are adverse to

federal law and its objectives. Without the benefit of a definitive interpretation from the state courts, it would be inappropriate to assume §2(B) will be construed in a way that conflicts with federal law. 

Cf. Fox v. Washington, 236 U. S. 273, 277. This opinion does not 

foreclose other preemption and constitutional challenges to the law

as interpreted and applied after it goes into effect. Pp. 22–24. 

641 F. 3d 339, affirmed in part, reversed in part, and remanded. 

KENNEDY, J., delivered the opinion of the Court, in which ROBERTS, 

C. J., and GINSBURG, BREYER, and SOTOMAYOR, JJ., joined. SCALIA, J., 

THOMAS, J., and ALITO, J., filed opinions concurring in part and dissenting in part. KAGAN, J., took no part in the consideration or decision of 

the case. 
 

 

_________________ 

_________________ 


 


 

Cite as: 567 U. S. ____ (2012) 1 

Opinion of the Court 

NOTICE: This opinion is subject to formal revision before publication in the

preliminary print of the United States Reports. Readers are requested to

notify the Reporter of Decisions, Supreme Court of the United States, Washington, D. C. 20543, of any typographical or other formal errors, in order

that corrections may be made before the preliminary print goes to press. 

SUPREME COURT OF THE UNITED STATES 

No. 11–182 

ARIZONA, ET AL., PETITIONERS v. UNITED STATES 

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
 

APPEALS FOR THE NINTH CIRCUIT
 

[June 25, 2012] 

JUSTICE KENNEDY delivered the opinion of the Court. 

To address pressing issues related to the large number

of aliens within its borders who do not have a lawful right

to be in this country, the State of Arizona in 2010 enacted 

a statute called the Support Our Law Enforcement and 

Safe Neighborhoods Act. The law is often referred to as 

S. B. 1070, the version introduced in the state senate. See 

also H. 2162 (2010) (amending S. 1070). Its stated purpose is to “discourage and deter the unlawful entry and

presence of aliens and economic activity by persons unlawfully present in the United States.” Note following Ariz.

Rev. Stat. Ann. §11–1051 (West 2012). The law’s provisions establish an official state policy of “attrition through 

enforcement.” Ibid. The question before the Court is

whether federal law preempts and renders invalid four 

separate provisions of the state law. 

I 

The United States filed this suit against Arizona, seeking to enjoin S. B. 1070 as preempted. Four provisions of 

the law are at issue here. Two create new state offenses. 

Section 3 makes failure to comply with federal alienregistration requirements a state misdemeanor. Ariz. 
 

 


 

2 ARIZONA v. UNITED STATES 

Opinion of the Court 

Rev. Stat. Ann. §13–1509 (West Supp. 2011). Section 5, in 

relevant part, makes it a misdemeanor for an unauthorized alien to seek or engage in work in the State; this 

provision is referred to as §5(C). See §13–2928(C). Two 

other provisions give specific arrest authority and investigative duties with respect to certain aliens to state and

local law enforcement officers. Section 6 authorizes officers to arrest without a warrant a person “the officer has 

probable cause to believe . . . has committed any public 

offense that makes the person removable from the United 

States.” §13–3883(A)(5). Section 2(B) provides that officers who conduct a stop, detention, or arrest must in some 

circumstances make efforts to verify the person’s immigration status with the Federal Government. See §11–

1051(B) (West 2012).

The United States District Court for the District of 

Arizona issued a preliminary injunction preventing the

four provisions at issue from taking effect. 703 F. Supp. 

2d 980, 1008 (2010). The Court of Appeals for the Ninth

Circuit affirmed. 641 F. 3d 339, 366 (2011). It agreed that

the United States had established a likelihood of success 

on its preemption claims. The Court of Appeals was unanimous in its conclusion that §§3 and 5(C) were likely 

preempted. Judge Bea dissented from the decision to 

uphold the preliminary injunction against §§2(B) and 6.

This Court granted certiorari to resolve important questions concerning the interaction of state and federal power

with respect to the law of immigration and alien status.

565 U. S. ___ (2011). 

II
 

A 

The Government of the United States has broad, undoubted power over the subject of immigration and the

status of aliens. See Toll v. Moreno, 458 U. S. 1, 10 (1982);

see generally S. Legomsky & C. Rodríguez, Immigration 
Cite as: 567 U. S. ____ (2012) 3 

Opinion of the Court 

and Refugee Law and Policy 115–132 (5th ed. 2009). This 

authority rests, in part, on the National Government’s 

constitutional power to “establish an uniform Rule of Naturalization,” U. S. Const., Art. I, §8, cl. 4, and its inherent power as sovereign to control and conduct relations 

with foreign nations, see Toll, supra, at 10 (citing United 

States v. Curtiss-Wright Export Corp., 299 U. S. 304, 318 

(1936)).

The federal power to determine immigration policy is

well settled. Immigration policy can affect trade, investment, tourism, and diplomatic relations for the entire

Nation, as well as the perceptions and expectations of 

aliens in this country who seek the full protection of its 

laws. See, e.g., Brief for Argentina et al. as Amici Curiae; 

see also Harisiades v. Shaughnessy, 342 U. S. 580, 

588–589 (1952). Perceived mistreatment of aliens in the 

United States may lead to harmful reciprocal treatment

of American citizens abroad. See Brief for Madeleine K. 

Albright et al. as Amici Curiae 24–30. 

It is fundamental that foreign countries concerned about 

the status, safety, and security of their nationals in the 

United States must be able to confer and communicate on 

this subject with one national sovereign, not the 50 separate States. See Chy Lung v. Freeman, 92 U. S. 275, 279– 

280 (1876); see also The Federalist No. 3, p. 39 (C. Rossiter 

ed. 2003) (J. Jay) (observing that federal power would be

necessary in part because “bordering States . . . under the

impulse of sudden irritation, and a quick sense of apparent interest or injury” might take action that would undermine foreign relations). This Court has reaffirmed that 

“[o]ne of the most important and delicate of all international relationships . . . has to do with the protection of the

just rights of a country’s own nationals when those nationals are in another country.” Hines v. Davidowitz, 312 

U. S. 52, 64 (1941).

Federal governance of immigration and alien status is 
 

4 ARIZONA v. UNITED STATES 

Opinion of the Court 

extensive and complex. Congress has specified categories of aliens who may not be admitted to the United

States. See 8 U. S. C. §1182. Unlawful entry and unlawful

reentry into the country are federal offenses. §§1325, 

1326. Once here, aliens are required to register with the

Federal Government and to carry proof of status on their 

person. See §§1301–1306. Failure to do so is a federal 

misdemeanor. §§1304(e), 1306(a). Federal law also authorizes States to deny noncitizens a range of public benefits, §1622; and it imposes sanctions on employers who

hire unauthorized workers, §1324a.

Congress has specified which aliens may be removed

from the United States and the procedures for doing so. 

Aliens may be removed if they were inadmissible at the

time of entry, have been convicted of certain crimes, or

meet other criteria set by federal law. See §1227. Removal is a civil, not criminal, matter. A principal feature of 

the removal system is the broad discretion exercised by

immigration officials. See Brief for Former Commissioners of the United States Immigration and Naturalization

Service as Amici Curiae 8–13 (hereinafter Brief for Former INS Commissioners). Federal officials, as an initial 

matter, must decide whether it makes sense to pursue 

removal at all. If removal proceedings commence, aliens

may seek asylum and other discretionary relief allowing

them to remain in the country or at least to leave without

formal removal. See §1229a(c)(4); see also, e.g., §§1158

(asylum), 1229b (cancellation of removal), 1229c (voluntary departure). 

Discretion in the enforcement of immigration law embraces immediate human concerns. Unauthorized workers trying to support their families, for example, likely

pose less danger than alien smugglers or aliens who commit a serious crime. The equities of an individual case

may turn on many factors, including whether the alien

has children born in the United States, long ties to the 
 

 

 

Cite as: 567 U. S. ____ (2012) 5 

Opinion of the Court 

community, or a record of distinguished military service.

Some discretionary decisions involve policy choices that

bear on this Nation’s international relations. Returning

an alien to his own country may be deemed inappropriate

even where he has committed a removable offense or fails 

to meet the criteria for admission. The foreign state may

be mired in civil war, complicit in political persecution, or 

enduring conditions that create a real risk that the alien

or his family will be harmed upon return. The dynamic

nature of relations with other countries requires the Executive Branch to ensure that enforcement policies are consistent with this Nation’s foreign policy with respect to

these and other realities. 

Agencies in the Department of Homeland Security play

a major role in enforcing the country’s immigration laws. 

United States Customs and Border Protection (CBP) is responsible for determining the admissibility of aliens and 

securing the country’s borders. See Dept. of Homeland

Security, Office of Immigration Statistics, Immigration

Enforcement Actions: 2010, p. 1 (2011). In 2010, CBP’s 

Border Patrol apprehended almost half a million people. 

Id., at 3. Immigration and Customs Enforcement (ICE), a 

second agency, “conducts criminal investigations involving 

the enforcement of immigration-related statutes.” Id., at 

2. ICE also operates the Law Enforcement Support Center. LESC, as the Center is known, provides immigration status information to federal, state, and local officials 

around the clock. See App. 91. ICE officers are responsible “for the identification, apprehension, and removal of

illegal aliens from the United States.” Immigration Enforcement Actions, supra, at 2. Hundreds of thousands of 

aliens are removed by the Federal Government every year.

See id., at 4 (reporting there were 387,242 removals, and 

476,405 returns without a removal order, in 2010). 
 

 

 

6 ARIZONA v. UNITED STATES 

Opinion of the Court 

B 

The pervasiveness of federal regulation does not diminish the importance of immigration policy to the States. 

Arizona bears many of the consequences of unlawful immigration. Hundreds of thousands of deportable aliens

are apprehended in Arizona each year. Dept. of Homeland 

Security, Office of Immigration Statistics, 2010 Yearbook 

of Immigration Statistics 93 (2011) (Table 35). Unauthorized aliens who remain in the State comprise, by one estimate, almost six percent of the population. See Passel 

& Cohn, Pew Hispanic Center, U. S. Unauthorized Immigration Flows Are Down Sharply Since Mid-Decade 3

(2010). And in the State’s most populous county, these

aliens are reported to be responsible for a disproportionate

share of serious crime. See, e.g., Camarota & Vaughan, 

Center for Immigration Studies, Immigration and Crime: 

Assessing a Conflicted Situation 16 (2009) (Table 3) (estimating that unauthorized aliens comprise 8.9% of the

population and are responsible for 21.8% of the felonies in 

Maricopa County, which includes Phoenix). 

Statistics alone do not capture the full extent of Arizona’s concerns. Accounts in the record suggest there is an

“epidemic of crime, safety risks, serious property damage, 

and environmental problems” associated with the influx

of illegal migration across private land near the Mexican 

border. Brief for Petitioners 6. Phoenix is a major city of

the United States, yet signs along an interstate highway

30 miles to the south warn the public to stay away. One 

reads, “DANGER—PUBLIC WARNING—TRAVEL NOT 

RECOMMENDED / Active Drug and Human Smuggling 

Area / Visitors May Encounter Armed Criminals and 

Smuggling Vehicles Traveling at High Rates of Speed.”

App. 170; see also Brief for Petitioners 5–6. The problems

posed to the State by illegal immigration must not be 

underestimated. 

These concerns are the background for the formal legal 
 

Cite as: 567 U. S. ____ (2012) 7 

Opinion of the Court 

analysis that follows. The issue is whether, under preemption principles, federal law permits Arizona to implement the state-law provisions in dispute. 

III 

Federalism, central to the constitutional design, adopts

the principle that both the National and State Governments have elements of sovereignty the other is bound to 

respect. See Gregory v. Ashcroft, 501 U. S. 452, 457 

(1991); U. S. Term Limits, Inc. v. Thornton, 514 U. S. 779, 

838 (1995) (KENNEDY, J., concurring). From the existence 

of two sovereigns follows the possibility that laws can be 

in conflict or at cross-purposes. The Supremacy Clause 

provides a clear rule that federal law “shall be the supreme Law of the Land; and the Judges in every State

shall be bound thereby, any Thing in the Constitution or

Laws of any State to the Contrary notwithstanding.” 

Art. VI, cl. 2. Under this principle, Congress has the

power to preempt state law. See Crosby v. National Foreign Trade Council, 530 U. S. 363, 372 (2000); Gibbons 

v. Ogden, 9 Wheat. 1, 210–211 (1824). There is no doubt 

that Congress may withdraw specified powers from the

States by enacting a statute containing an express 

preemption provision. See, e.g., Chamber of Commerce of 

United States of America v. Whiting, 563 U. S. ___, ___ 

(2011) (slip op., at 4). 

State law must also give way to federal law in at least

two other circumstances. First, the States are precluded 

from regulating conduct in a field that Congress, acting 

within its proper authority, has determined must be regulated by its exclusive governance. See Gade v. National 

Solid Wastes Management Assn., 505 U. S. 88, 115 (1992).

The intent to displace state law altogether can be inferred

from a framework of regulation “so pervasive . . . that 

Congress left no room for the States to supplement it” or

where there is a “federal interest . . . so dominant that the 
 

8 ARIZONA v. UNITED STATES 

Opinion of the Court 

federal system will be assumed to preclude enforcement of 

state laws on the same subject.” Rice v. Santa Fe Elevator 

Corp., 331 U. S. 218, 230 (1947); see English v. General 

Elec. Co., 496 U. S. 72, 79 (1990). 

Second, state laws are preempted when they conflict 

with federal law. Crosby, supra, at 372. This includes 

cases where “compliance with both federal and state

regulations is a physical impossibility,” Florida Lime & 

Avocado Growers, Inc. v. Paul, 373 U. S. 132, 142–143 

(1963), and those instances where the challenged state law 

“stands as an obstacle to the accomplishment and execution of the full purposes and objectives of Congress,” 

Hines, 312 U. S., at 67; see also Crosby, supra, at 373 

(“What is a sufficient obstacle is a matter of judgment, to

be informed by examining the federal statute as a whole 

and identifying its purpose and intended effects”). In 

preemption analysis, courts should assume that “the 

historic police powers of the States” are not superseded 

“unless that was the clear and manifest purpose of Congress.” Rice, supra, at 230; see Wyeth v. Levine, 555 U. S. 

555, 565 (2009).

The four challenged provisions of the state law each 

must be examined under these preemption principles. 

IV 

A 

Section 3 

Section 3 of S. B. 1070 creates a new state misdemeanor. It forbids the “willful failure to complete or carry an 

alien registration document . . . in violation of 8 United 

States Code section 1304(e) or 1306(a).” Ariz. Rev. Stat. 

Ann. §11–1509(A) (West Supp. 2011). In effect, §3 adds a 

state-law penalty for conduct proscribed by federal law. 

The United States contends that this state enforcement 

mechanism intrudes on the field of alien registration, a 

field in which Congress has left no room for States to 
 

 

 

Cite as: 567 U. S. ____ (2012) 9 

Opinion of the Court 

regulate. See Brief for United States 27, 31. 

The Court discussed federal alien-registration requirements in Hines v. Davidowitz, 312 U. S. 52. In 1940, as 

international conflict spread, Congress added to federal 

immigration law a “complete system for alien registration.” Id., at 70. The new federal law struck a careful 

balance. It punished an alien’s willful failure to register 

but did not require aliens to carry identification cards.

There were also limits on the sharing of registration records and fingerprints. The Court found that Congress

intended the federal plan for registration to be a “single

integrated and all-embracing system.” Id., at 74. Because 

this “complete scheme . . . for the registration of aliens”

touched on foreign relations, it did not allow the States to 

“curtail or complement” federal law or to “enforce additional or auxiliary regulations.” Id., at 66–67. As a consequence, the Court ruled that Pennsylvania could not 

enforce its own alien-registration program. See id., at 59, 74. 

The present regime of federal regulation is not identical to the statutory framework considered in Hines, but 

it remains comprehensive. Federal law now includes a 

requirement that aliens carry proof of registration. 8 

U. S. C. §1304(e). Other aspects, however, have stayed the 

same. Aliens who remain in the country for more than 30

days must apply for registration and be fingerprinted.

Compare §1302(a) with id., §452(a) (1940 ed.). Detailed 

information is required, and any change of address has 

to be reported to the Federal Government. Compare 

§§1304(a), 1305(a) (2006 ed.), with id., §§455(a), 456 (1940 

ed.). The statute continues to provide penalties for the

willful failure to register. Compare §1306(a) (2006 ed.), 

with id., §457 (1940 ed.).

The framework enacted by Congress leads to the conclusion here, as it did in Hines, that the Federal Government 

has occupied the field of alien registration. See American 

Ins. Assn. v. Garamendi, 539 U. S. 396, 419, n. 11 (2003) 
 

10 ARIZONA v. UNITED STATES 

Opinion of the Court 

(characterizing Hines as a field preemption case); Pennsylvania v. Nelson, 350 U. S. 497, 504 (1956) (same); see also

Dinh, Reassessing the Law of Preemption, 88 Geo. L. J.

2085, 2098–2099, 2107 (2000) (same). The federal statutory directives provide a full set of standards governing

alien registration, including the punishment for noncompliance. It was designed as a “‘harmonious whole.’” 

Hines, supra, at 72. Where Congress occupies an entire

field, as it has in the field of alien registration, even complementary state regulation is impermissible. Field preemption reflects a congressional decision to foreclose any 

state regulation in the area, even if it is parallel to federal standards. See Silkwood v. Kerr-McGee Corp., 464 

U. S. 238, 249 (1984).

Federal law makes a single sovereign responsible for 

maintaining a comprehensive and unified system to keep

track of aliens within the Nation’s borders. If §3 of the

Arizona statute were valid, every State could give itself

independent authority to prosecute federal registration

violations, “diminish[ing] the [Federal Government]’s control 

over enforcement” and “detract[ing] from the ‘integrated 

scheme of regulation’ created by Congress.” Wisconsin 

Dept. of Industry v. Gould Inc., 475 U. S. 282, 288–289 

(1986). Even if a State may make violation of federal 

law a crime in some instances, it cannot do so in a field 

(like the field of alien registration) that has been occupied 

by federal law. See California v. Zook, 336 U. S. 725, 730– 

731, 733 (1949); see also In re Loney, 134 U. S. 372, 375– 

376 (1890) (States may not impose their own punishment

for perjury in federal courts).

Arizona contends that §3 can survive preemption because the provision has the same aim as federal law and 

adopts its substantive standards. This argument not only

ignores the basic premise of field preemption—that States 

may not enter, in any respect, an area the Federal Government has reserved for itself—but also is unpersuasive 
Cite as: 567 U. S. ____ (2012) 11 

Opinion of the Court 

on its own terms. Permitting the State to impose its own

penalties for the federal offenses here would conflict with

the careful framework Congress adopted. Cf. Buckman 

Co. v. Plaintiffs’ Legal Comm., 531 U. S. 341, 347–348 

(2001) (States may not impose their own punishment for 

fraud on the Food and Drug Administration); Wisconsin 

Dept., supra, at 288 (States may not impose their own 

punishment for repeat violations of the National Labor 

Relations Act). Were §3 to come into force, the State

would have the power to bring criminal charges against 

individuals for violating a federal law even in circumstances where federal officials in charge of the comprehensive scheme determine that prosecution would frustrate 

federal policies.

There is a further intrusion upon the federal scheme. 

Even where federal authorities believe prosecution is appropriate, there is an inconsistency between §3 and federal law with respect to penalties. Under federal law, 

the failure to carry registration papers is a misdemeanor 

that may be punished by a fine, imprisonment, or a term 

of probation. See 8 U. S. C. §1304(e) (2006 ed.); 18 U. S. C. 

§3561. State law, by contrast, rules out probation as a

possible sentence (and also eliminates the possibility of

a pardon). See Ariz. Rev. Stat. Ann. §13–1509(D) (West 

Supp. 2011). This state framework of sanctions creates a 

conflict with the plan Congress put in place. See Wisconsin Dept., supra, at 286 (“[C]onflict is imminent whenever

two separate remedies are brought to bear on the same 

activity” (internal quotation marks omitted)). 

These specific conflicts between state and federal law 

simply underscore the reason for field preemption. As it 

did in Hines, the Court now concludes that, with respect

to the subject of alien registration, Congress intended to

preclude States from “complement[ing] the federal law, or 

enforc[ing] additional or auxiliary regulations.” 312 U. S., 

at 66–67. Section 3 is preempted by federal law. 
 

 

12 ARIZONA v. UNITED STATES 

Opinion of the Court 

B 

Section 5(C) 

Unlike §3, which replicates federal statutory requirements, §5(C) enacts a state criminal prohibition where no

federal counterpart exists. The provision makes it a state

misdemeanor for “an unauthorized alien to knowingly apply for work, solicit work in a public place or perform 

work as an employee or independent contractor” in Arizona. Ariz. Rev. Stat. Ann. §13–2928(C) (West Supp. 2011).

Violations can be punished by a $2,500 fine and incarceration for up to six months. See §13–2928(F); see also 

§§13–707(A)(1) (West 2010); 13–802(A); 13–902(A)(5). The 

United States contends that the provision upsets the balance struck by the Immigration Reform and Control Act 

of 1986 (IRCA) and must be preempted as an obstacle

to the federal plan of regulation and control.

When there was no comprehensive federal program 

regulating the employment of unauthorized aliens, this 

Court found that a State had authority to pass its own

laws on the subject. In 1971, for example, California

passed a law imposing civil penalties on the employment 

of aliens who were “not entitled to lawful residence in the 

United States if such employment would have an adverse

effect on lawful resident workers.” 1971 Cal. Stats. ch. 

1442, §1(a). The law was upheld against a preemption 

challenge in De Canas v. Bica, 424 U. S. 351 (1976). De 

Canas recognized that “States possess broad authority

under their police powers to regulate the employment

relationship to protect workers within the State.” Id., at 

356. At that point, however, the Federal Government had 

expressed no more than “a peripheral concern with [the] 

employment of illegal entrants.” Id., at 360; see Whiting, 

563 U. S., at ___ (slip op., at 3). 

Current federal law is substantially different from the

regime that prevailed when De Canas was decided. Congress enacted IRCA as a comprehensive framework for 
 

Cite as: 567 U. S. ____ (2012) 13 

Opinion of the Court 

“combating the employment of illegal aliens.” Hoffman 

Plastic Compounds, Inc. v. NLRB, 535 U. S. 137, 147 

(2002). The law makes it illegal for employers to knowingly hire, recruit, refer, or continue to employ unauthorized 

workers. See 8 U. S. C. §§1324a(a)(1)(A), (a)(2). It also 

requires every employer to verify the employment authorization status of prospective employees. See §§1324a(a)

(1)(B), (b); 8 CFR §274a.2(b) (2012). These requirements

are enforced through criminal penalties and an escalating series of civil penalties tied to the number of times

an employer has violated the provisions. See 8 U. S. C. 

§§1324a(e)(4), (f); 8 CFR §274a.10. 

This comprehensive framework does not impose federal 

criminal sanctions on the employee side (i.e., penalties on

aliens who seek or engage in unauthorized work). Under 

federal law some civil penalties are imposed instead. With 

certain exceptions, aliens who accept unlawful employment are not eligible to have their status adjusted to

that of a lawful permanent resident. See 8 U. S. C. 

§§1255(c)(2), (c)(8). Aliens also may be removed from the

country for having engaged in unauthorized work. See 

§1227(a)(1)(C)(i); 8 CFR §214.1(e). In addition to specifying these civil consequences, federal law makes it a crime 

for unauthorized workers to obtain employment through

fraudulent means. See 18 U. S. C. §1546(b). Congress has

made clear, however, that any information employees

submit to indicate their work status “may not be used” for

purposes other than prosecution under specified federal

criminal statutes for fraud, perjury, and related conduct.

See 8 U. S. C. §§1324a(b)(5), (d)(2)(F)–(G).

The legislative background of IRCA underscores the fact

that Congress made a deliberate choice not to impose crim

inal penalties on aliens who seek, or engage in, unauthorized employment. A commission established by Congress 

to study immigration policy and to make recommendations concluded these penalties would be “unnecessary 

­
 

 

14 ARIZONA v. UNITED STATES 

Opinion of the Court 

and unworkable.” U. S. Immigration Policy and the National Interest: The Final Report and Recommendations of

the Select Commission on Immigration and Refugee Policy 

with Supplemental Views by Commissioners 65–66 (1981); 

see Pub. L. 95–412, §4, 92 Stat. 907. Proposals to make

unauthorized work a criminal offense were debated and 

discussed during the long process of drafting IRCA. See 

Brief for Service Employees International Union et al. as 

Amici Curiae 9–12. But Congress rejected them. See, e.g.,

119 Cong. Rec. 14184 (1973) (statement of Rep. Dennis). 

In the end, IRCA’s framework reflects a considered judgment that making criminals out of aliens engaged in 

unauthorized work—aliens who already face the possibility of employer exploitation because of their removable 

status—would be inconsistent with federal policy and objectives. See, e.g., Hearings before the Subcommittee 

No. 1 of the House Committee on the Judiciary, 92d Cong., 

1st Sess., pt. 3, pp. 919–920 (1971) (statement of Rep.

Rodino, the eventual sponsor of IRCA in the House of 

Representatives).

IRCA’s express preemption provision, which in most

instances bars States from imposing penalties on employers of unauthorized aliens, is silent about whether additional penalties may be imposed against the employees 

themselves. See 8 U. S. C. §1324a(h)(2); Whiting, supra,

at ___–___ (slip op., at 1–2). But the existence of an “express pre-emption provisio[n] does not bar the ordinary

working of conflict pre-emption principles” or impose a 

“special burden” that would make it more difficult to

establish the preemption of laws falling outside the clause. 

Geier v. American Honda Motor Co., 529 U. S. 861, 869– 

872 (2000); see Sprietsma v. Mercury Marine, 537 U. S. 51, 

65 (2002).

The ordinary principles of preemption include the wellsettled proposition that a state law is preempted where it 

“stands as an obstacle to the accomplishment and exe­
Cite as: 567 U. S. ____ (2012) 15 

Opinion of the Court 

cution of the full purposes and objectives of Congress.” 

Hines, 312 U. S., at 67. Under §5(C) of S. B. 1070, Arizona 

law would interfere with the careful balance struck by

Congress with respect to unauthorized employment of 

aliens. Although §5(C) attempts to achieve one of the 

same goals as federal law—the deterrence of unlawful 

employment—it involves a conflict in the method of enforcement. The Court has recognized that a “[c]onflict 

in technique can be fully as disruptive to the system Congress enacted as conflict in overt policy.” Motor Coach 

Employees v. Lockridge, 403 U. S. 274, 287 (1971). The 

correct instruction to draw from the text, structure, and 

history of IRCA is that Congress decided it would be inappropriate to impose criminal penalties on aliens who seek 

or engage in unauthorized employment. It follows that a 

state law to the contrary is an obstacle to the regulatory

system Congress chose. See Puerto Rico Dept. of Consumer Affairs v. ISLA Petroleum Corp., 485 U. S. 495, 503 

(1988) (“Where a comprehensive federal scheme intentionally leaves a portion of the regulated field without controls, then the pre-emptive inference can be drawn—not 

from federal inaction alone, but from inaction joined with

action”). Section 5(C) is preempted by federal law. 

C 

Section 6 

Section 6 of S. B. 1070 provides that a state officer,

“without a warrant, may arrest a person if the officer has 

probable cause to believe . . . [the person] has committed 

any public offense that makes [him] removable from the

United States.” Ariz. Rev. Stat. Ann. §13–3883(A)(5) 

(West Supp. 2011). The United States argues that arrests

authorized by this statute would be an obstacle to the 

removal system Congress created.

As a general rule, it is not a crime for a removable alien 

to remain present in the United States. See INS v. Lopez-
 

 

 

 

16 ARIZONA v. UNITED STATES 

Opinion of the Court 

Mendoza, 468 U. S. 1032, 1038 (1984). If the police stop

someone based on nothing more than possible removability, the usual predicate for an arrest is absent. When an 

alien is suspected of being removable, a federal official

issues an administrative document called a Notice to Appear. See 8 U. S. C. §1229(a); 8 CFR §239.1(a) (2012).

The form does not authorize an arrest. Instead, it gives

the alien information about the proceedings, including the 

time and date of the removal hearing. See 8 U. S. C. 

§1229(a)(1). If an alien fails to appear, an in absentia 

order may direct removal. §1229a(5)(A). 

The federal statutory structure instructs when it is appropriate to arrest an alien during the removal process. 

For example, the Attorney General can exercise discretion 

to issue a warrant for an alien’s arrest and detention 

“pending a decision on whether the alien is to be removed

from the United States.” 8 U. S. C. §1226(a); see Memorandum from John Morton, Director, ICE, to All Field 

Office Directors et al., Exercising Prosecutorial Discretion 

Consistent with the Civil Immigration Enforcement Priorities of the Agency for the Apprehension, Detention, and 

Removal of Aliens (June 17, 2011) (hereinafter 2011 ICE

Memorandum) (describing factors informing this and related decisions). And if an alien is ordered removed after 

a hearing, the Attorney General will issue a warrant. 

See 8 CFR §241.2(a)(1). In both instances, the warrants 

are executed by federal officers who have received training 

in the enforcement of immigration law. See §§241.2(b), 

287.5(e)(3). If no federal warrant has been issued, those 

officers have more limited authority. See 8 U. S. C. §1357(a). 

They may arrest an alien for being “in the United 

States in violation of any [immigration] law or regulation,” for example, but only where the alien “is likely to

escape before a warrant can be obtained.” §1357(a)(2). 

Section 6 attempts to provide state officers even greater

authority to arrest aliens on the basis of possible remova­
Cite as: 567 U. S. ____ (2012) 17 

Opinion of the Court 

bility than Congress has given to trained federal immigration officers. Under state law, officers who believe 

an alien is removable by reason of some “public offense” 

would have the power to conduct an arrest on that basis

regardless of whether a federal warrant has issued or

the alien is likely to escape. This state authority could be

exercised without any input from the Federal Government

about whether an arrest is warranted in a particular case. 

This would allow the State to achieve its own immigration policy. The result could be unnecessary harassment

of some aliens (for instance, a veteran, college student, or 

someone assisting with a criminal investigation) whom 

federal officials determine should not be removed. 

This is not the system Congress created. Federal law 

specifies limited circumstances in which state officers may 

perform the functions of an immigration officer. A principal example is when the Attorney General has granted 

that authority to specific officers in a formal agreement 

with a state or local government. See §1357(g)(1); see also

§1103(a)(10) (authority may be extended in the event of an

“imminent mass influx of aliens off the coast of the United 

States”); §1252c (authority to arrest in specific circumstance after consultation with the Federal Government);

§1324(c) (authority to arrest for bringing in and harboring 

certain aliens). Officers covered by these agreements are

subject to the Attorney General’s direction and supervision. §1357(g)(3). There are significant complexities

involved in enforcing federal immigration law, including 

the determination whether a person is removable. See 

Padilla v. Kentucky, 559 U. S. ___, ___–___ (2010) (ALITO, 

J., concurring in judgment) (slip op., at 4–7). As a result, 

the agreements reached with the Attorney General must 

contain written certification that officers have received 

adequate training to carry out the duties of an immigration officer. See §1357(g)(2); cf. 8 CFR §§287.5(c) (arrest power contingent on training), 287.1(g) (defining the 
 

18 ARIZONA v. UNITED STATES 

Opinion of the Court 

training).

By authorizing state officers to decide whether an 

alien should be detained for being removable, §6 violates

the principle that the removal process is entrusted to the

discretion of the Federal Government. See, e.g., Reno v. 

American-Arab Anti-Discrimination Comm., 525 U. S. 471, 

483–484 (1999); see also Brief for Former INS Commissioners 8–13. A decision on removability requires a determination whether it is appropriate to allow a foreign 

national to continue living in the United States. Decisions 

of this nature touch on foreign relations and must be made

with one voice. See Jama v. Immigration and Customs 

Enforcement, 543 U. S. 335, 348 (2005) (“Removal decisions, including the selection of a removed alien’s destination, may implicate [the Nation’s] relations with foreign

powers and require consideration of changing political and 

economic circumstances” (internal quotation marks omitted)); see also Galvan v. Press, 347 U. S. 522, 531 (1954) 

(“Policies pertaining to the entry of aliens and their right

to remain here are . . . entrusted exclusively to Congress

. . .”); Truax v. Raich, 239 U. S. 33, 42 (1915) (“The authority to control immigration—to admit or exclude aliens—is

vested solely in the Federal Government”).

In defense of §6, Arizona notes a federal statute permitting state officers to “cooperate with the Attorney General 

in the identification, apprehension, detention, or removal 

of aliens not lawfully present in the United States.” 8 

U. S. C. §1357(g)(10)(B). There may be some ambiguity as

to what constitutes cooperation under the federal law; but 

no coherent understanding of the term would incorporate

the unilateral decision of state officers to arrest an alien 

for being removable absent any request, approval, or other 

instruction from the Federal Government. The Department of Homeland Security gives examples of what would 

constitute cooperation under federal law. These include 

situations where States participate in a joint task force 
Cite as: 567 U. S. ____ (2012) 19 

Opinion of the Court 

with federal officers, provide operational support in executing a warrant, or allow federal immigration officials 

to gain access to detainees held in state facilities. See 

Dept. of Homeland Security, Guidance on State and Local 

Governments’ Assistance in Immigration Enforcement 

and Related Matters 13–14 (2011), online at http://

www.dhs.gov/files/resources/immigration.shtm (all Internet materials as visited June 21, 2012, and available in 

Clerk of Court’s case file). State officials can also assist 

the Federal Government by responding to requests for 

information about when an alien will be released from 

their custody. See §1357(d). But the unilateral state 

action to detain authorized by §6 goes far beyond these

measures, defeating any need for real cooperation.

Congress has put in place a system in which state officers may not make warrantless arrests of aliens based on

possible removability except in specific, limited circumstances. By nonetheless authorizing state and local officers to engage in these enforcement activities as a general

matter, §6 creates an obstacle to the full purposes and

objectives of Congress. See Hines, 312 U. S., at 67. Section 6 is preempted by federal law. 

D 

Section 2(B) 

Section 2(B) of S. B. 1070 requires state officers to make

a “reasonable attempt . . . to determine the immigration

status” of any person they stop, detain, or arrest on some

other legitimate basis if “reasonable suspicion exists that 

the person is an alien and is unlawfully present in the

United States.” Ariz. Rev. Stat. Ann. §11–1051(B) (West 

2012). The law also provides that “[a]ny person who is 

arrested shall have the person’s immigration status determined before the person is released.” Ibid. The accepted

way to perform these status checks is to contact ICE,

which maintains a database of immigration records. 
 

20 ARIZONA v. UNITED STATES 

Opinion of the Court 

Three limits are built into the state provision. First, a 

detainee is presumed not to be an alien unlawfully present 

in the United States if he or she provides a valid Arizona 

driver’s license or similar identification. Second, officers 

“may not consider race, color or national origin . . . except 

to the extent permitted by the United States [and] Arizona Constitution[s].” Ibid. Third, the provisions must 

be “implemented in a manner consistent with federal law 

regulating immigration, protecting the civil rights of all 

persons and respecting the privileges and immunities of

United States citizens.” §11–1051(L) (West 2012). 

The United States and its amici contend that, even with 

these limits, the State’s verification requirements pose an

obstacle to the framework Congress put in place. The first 

concern is the mandatory nature of the status checks. The 

second is the possibility of prolonged detention while the

checks are being performed. 

1 

Consultation between federal and state officials is an 

important feature of the immigration system. Congress

has made clear that no formal agreement or special training needs to be in place for state officers to “communicate

with the [Federal Government] regarding the immigration

status of any individual, including reporting knowledge

that a particular alien is not lawfully present in the United

States.” 8 U. S. C. §1357(g)(10)(A). And Congress has

obligated ICE to respond to any request made by state

officials for verification of a person’s citizenship or immigration status. See §1373(c); see also §1226(d)(1)(A) 

(requiring a system for determining whether individuals

arrested for aggravated felonies are aliens). ICE’s Law 

Enforcement Support Center operates “24 hours a day, 

seven days a week, 365 days a year” and provides, among

other things, “immigration status, identity information

and real-time assistance to local, state and federal law 
 

Cite as: 567 U. S. ____ (2012) 21 

Opinion of the Court 

enforcement agencies.” ICE, Fact Sheet: Law Enforcement Support Center (May 29, 2012), online at http://

www.ice.gov/news/library/factsheets/lesc.htm. LESC re

sponded to more than one million requests for information 

in 2009 alone. App. 93.

The United States argues that making status verification mandatory interferes with the federal immigration

scheme. It is true that §2(B) does not allow state officers 

to consider federal enforcement priorities in deciding

whether to contact ICE about someone they have detained. See Brief for United States 47–50. In other words, 

the officers must make an inquiry even in cases where it 

seems unlikely that the Attorney General would have 

the alien removed. This might be the case, for example,

when an alien is an elderly veteran with significant and 

longstanding ties to the community. See 2011 ICE Memorandum 4–5 (mentioning these factors as relevant).

Congress has done nothing to suggest it is inappropriate

to communicate with ICE in these situations, however. 

Indeed, it has encouraged the sharing of information about 

possible immigration violations. See 8 U. S. C. §1357(g) 

(10)(A). A federal statute regulating the public benefits

provided to qualified aliens in fact instructs that “no State

or local government entity may be prohibited, or in any 

way restricted, from sending to or receiving from [ICE]

information regarding the immigration status, lawful or 

unlawful, of an alien in the United States.” §1644. The 

federal scheme thus leaves room for a policy requiring

state officials to contact ICE as a routine matter. Cf. 

Whiting, 563 U. S., at ___–___ (slip op., at 23–24) (rejecting argument that federal law preempted Arizona’s requirement that employers determine whether employees

were eligible to work through the federal E-Verify system

where the Federal Government had encouraged its use). 

­
 

 

22 ARIZONA v. UNITED STATES 

Opinion of the Court 

2 

Some who support the challenge to §2(B) argue that, in 

practice, state officers will be required to delay the release 

of some detainees for no reason other than to verify their 

immigration status. See, e.g., Brief for Former Arizona 

Attorney General Terry Goddard et al. as Amici Curiae 37, 

n. 49. Detaining individuals solely to verify their immigration status would raise constitutional concerns. See, 

e.g., Arizona v. Johnson, 555 U. S. 323, 333 (2009); Illinois 

v. Caballes, 543 U. S. 405, 407 (2005) (“A seizure that is

justified solely by the interest in issuing a warning ticket 

to the driver can become unlawful if it is prolonged beyond

the time reasonably required to complete that mission”).

And it would disrupt the federal framework to put state

officers in the position of holding aliens in custody for

possible unlawful presence without federal direction and

supervision. Cf. Part IV–C, supra (concluding that Arizona may not authorize warrantless arrests on the basis of

removability). The program put in place by Congress does

not allow state or local officers to adopt this enforcement

mechanism. 

But §2(B) could be read to avoid these concerns. To take 

one example, a person might be stopped for jaywalking in 

Tucson and be unable to produce identification. The first 

sentence of §2(B) instructs officers to make a “reasonable” 

attempt to verify his immigration status with ICE if there

is reasonable suspicion that his presence in the United 

States is unlawful. The state courts may conclude that, 

unless the person continues to be suspected of some crime 

for which he may be detained by state officers, it would 

not be reasonable to prolong the stop for the immigration

inquiry. See Reply Brief for Petitioners 12, n. 4 (“[Section

2(B)] does not require the verification be completed during

the stop or detention if that is not reasonable or practicable”); cf. Muehler v. Mena, 544 U. S. 93, 101 (2005) (finding

no Fourth Amendment violation where questioning about 
 

Cite as: 567 U. S. ____ (2012) 23 

Opinion of the Court 

immigration status did not prolong a stop).

To take another example, a person might be held pending release on a charge of driving under the influence of

alcohol. As this goes beyond a mere stop, the arrestee

(unlike the jaywalker) would appear to be subject to the 

categorical requirement in the second sentence of §2(B)

that “[a]ny person who is arrested shall have the person’s 

immigration status determined before [he] is released.” 

State courts may read this as an instruction to initiate a

status check every time someone is arrested, or in some 

subset of those cases, rather than as a command to hold 

the person until the check is complete no matter the circumstances. Even if the law is read as an instruction to 

complete a check while the person is in custody, moreover, 

it is not clear at this stage and on this record that the 

verification process would result in prolonged detention.

However the law is interpreted, if §2(B) only requires 

state officers to conduct a status check during the course 

of an authorized, lawful detention or after a detainee has 

been released, the provision likely would survive preemption—at least absent some showing that it has other 

consequences that are adverse to federal law and its objectives. There is no need in this case to address whether 

reasonable suspicion of illegal entry or another immigration crime would be a legitimate basis for prolonging a

detention, or whether this too would be preempted by 

federal law. See, e.g., United States v. Di Re, 332 U. S. 

581, 589 (1948) (authority of state officers to make arrests

for federal crimes is, absent federal statutory instruction, 

a matter of state law); Gonzales v. Peoria, 722 F. 2d 468, 

475–476 (CA9 1983) (concluding that Arizona officers have

authority to enforce the criminal provisions of federal 

immigration law), overruled on other grounds in HodgersDurgin v. de la Vina, 199 F. 3d 1037 (CA9 1999). 

The nature and timing of this case counsel caution in

evaluating the validity of §2(B). The Federal Government 
 

 

24 ARIZONA v. UNITED STATES 

Opinion of the Court 

has brought suit against a sovereign State to challenge the

provision even before the law has gone into effect. There 

is a basic uncertainty about what the law means and how 

it will be enforced. At this stage, without the benefit of a 

definitive interpretation from the state courts, it would be 

inappropriate to assume §2(B) will be construed in a way

that creates a conflict with federal law. Cf. Fox v. Washington, 236 U. S. 273, 277 (1915) (“So far as statutes fairly 

may be construed in such a way as to avoid doubtful constitutional questions they should be so construed; and it is 

to be presumed that state laws will be construed in that 

way by the state courts” (citation omitted)). As a result, 

the United States cannot prevail in its current challenge. 

See Huron Portland Cement Co. v. Detroit, 362 U. S. 440, 

446 (1960) (“To hold otherwise would be to ignore the

teaching of this Court’s decisions which enjoin seeking out

conflicts between state and federal regulation where none 

clearly exists”). This opinion does not foreclose other 

preemption and constitutional challenges to the law as

interpreted and applied after it goes into effect. 

V 

Immigration policy shapes the destiny of the Nation.

On May 24, 2012, at one of this Nation’s most distinguished museums of history, a dozen immigrants stood 

before the tattered flag that inspired Francis Scott Key

to write the National Anthem. There they took the oath 

to become American citizens. The Smithsonian, News 

Release, Smithsonian Citizenship Ceremony Welcomes 

a Dozen New Americans (May 24, 2012), online at

http://newsdesk.si.edu/releases. These naturalization ceremonies bring together men and women of different origins who now share a common destiny. They swear a

common oath to renounce fidelity to foreign princes, to

defend the Constitution, and to bear arms on behalf of the 

country when required by law. 8 CFR §337.1(a) (2012). 
 

Cite as: 567 U. S. ____ (2012) 25 

Opinion of the Court 

The history of the United States is in part made of the

stories, talents, and lasting contributions of those who

crossed oceans and deserts to come here. 

The National Government has significant power to

regulate immigration. With power comes responsibility, 

and the sound exercise of national power over immigration 

depends on the Nation’s meeting its responsibility to base

its laws on a political will informed by searching, thoughtful, rational civic discourse. Arizona may have understandable frustrations with the problems caused by illegal 

immigration while that process continues, but the State 

may not pursue policies that undermine federal law. 

* * * 

The United States has established that §§3, 5(C), and 6

of S. B. 1070 are preempted. It was improper, however, to

enjoin §2(B) before the state courts had an opportunity to

construe it and without some showing that enforcement of

the provision in fact conflicts with federal immigration law 

and its objectives.

The judgment of the Court of Appeals for the Ninth 

Circuit is affirmed in part and reversed in part. The case 

is remanded for further proceedings consistent with this

opinion. 

It is so ordered.

 JUSTICE KAGAN took no part in the consideration or 

decision of this case. 
_________________ 

_________________ 


 


 

Cite as: 567 U. S. ____ (2012) 1 

Opinion of SCALIA, J. 

SUPREME COURT OF THE UNITED STATES 

No. 11–182 

ARIZONA, ET AL., PETITIONERS v. UNITED STATES 

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
 

APPEALS FOR THE NINTH CIRCUIT
 

[June 25, 2012] 

JUSTICE SCALIA, concurring in part and dissenting in 

part. 

The United States is an indivisible “Union of sovereign

States.” Hinderlider v. La Plata River & Cherry Creek 

Ditch Co., 304 U. S. 92, 104 (1938). Today’s opinion, approving virtually all of the Ninth Circuit’s injunction 

against enforcement of the four challenged provisions of 

Arizona’s law, deprives States of what most would consider the defining characteristic of sovereignty: the power 

to exclude from the sovereign’s territory people who have 

no right to be there. Neither the Constitution itself nor 

even any law passed by Congress supports this result. I 

dissent. 

I 

As a sovereign, Arizona has the inherent power to exclude persons from its territory, subject only to those 

limitations expressed in the Constitution or constitutionally imposed by Congress. That power to exclude has long

been recognized as inherent in sovereignty. Emer de 

Vattel’s seminal 1758 treatise on the Law of Nations 

stated: 

“The sovereign may forbid the entrance of his territory 

either to foreigners in general, or in particular cases,

or to certain persons, or for certain particular purposes, according as he may think it advantageous to 
 

2 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

the state. There is nothing in all this, that does not

flow from the rights of domain and sovereignty: every 

one is obliged to pay respect to the prohibition; and

whoever dares violate it, incurs the penalty decreed 

to render it effectual.” The Law of Nations, bk. II, 

ch. VII, §94, p. 309 (B. Kapossy & R. Whatmore eds. 

2008). 

See also I R. Phillimore, Commentaries upon International Law, pt. III, ch. X, p. 233 (1854) (“It is a received maxim

of International Law that, the Government of a State may 

prohibit the entrance of strangers into the country”).1 

There is no doubt that “before the adoption of the constitution of the United States” each State had the authority to “prevent [itself] from being burdened by an influx of

persons.” Mayor of New York v. Miln, 11 Pet. 102, 132– 

133 (1837). And the Constitution did not strip the States

of that authority. To the contrary, two of the Constitution’s provisions were designed to enable the States to

prevent “the intrusion of obnoxious aliens through other 

States.” Letter from James Madison to Edmund Randolph

(Aug. 27, 1782), in 1 The Writings of James Madison 226 

(1900); accord, The Federalist No. 42, pp. 269–271 (C.

Rossiter ed. 1961) (J. Madison). The Articles of Confeder­

—————— 

1Many of the 17th-, 18th-, and 19th-century commentators maintained that states should exclude foreigners only for good reason.

Pufendorf, for example, maintained that states are generally expected 

to grant “permanent settlement to strangers who have been driven 

from their former home,” though acknowledging that, when faced with 

the prospect of mass immigration, “every state may decide after its own

custom what privilege should be granted in such a situation.” 2 Of the 

Law of Nature and Nations, bk. III, ch. III, §10, p. 366 (C. Oldfather & 

W. Oldfather eds. 1934). See generally Cleveland, Powers Inherent in 

Sovereignty: Indians, Aliens, Territories, and the Nineteenth Century 

Origins of Plenary Power over Foreign Affairs, 81 Tex. L. Rev. 1, 83–87

(2002). But the authority to exclude was universally accepted as

inherent in sovereignty, whatever prudential limitations there might be

on its exercise. 
 

Cite as: 567 U. S. ____ (2012) 3 

Opinion of SCALIA, J. 

ation had provided that “the free inhabitants of each of 

these States, paupers, vagabonds and fugitives from justice excepted, shall be entitled to all privileges and immunities of free citizens in the several States.” Articles of 

Confederation, Art. IV. This meant that an unwelcome 

alien could obtain all the rights of a citizen of one State

simply by first becoming an inhabitant of another. To 

remedy this, the Constitution’s Privileges and Immunities

Clause provided that “[t]he Citizens of each State shall be 

entitled to all Privileges and Immunities of Citizens in the 

several States.” Art. IV, §2, cl. 1 (emphasis added). But 

if one State had particularly lax citizenship standards, it 

might still serve as a gateway for the entry of “obnoxious 

aliens” into other States. This problem was solved “by 

authorizing the general government to establish a uniform

rule of naturalization throughout the United States.” The 

Federalist No. 42, supra, at 271; see Art. I, §8, cl. 4. In 

other words, the naturalization power was given to Congress not to abrogate States’ power to exclude those they 

did not want, but to vindicate it. 

Two other provisions of the Constitution are an acknowledgment of the States’ sovereign interest in protecting their borders. Article I provides that “[n]o State shall, 

without the Consent of the Congress, lay any Imposts or

Duties on Imports or Exports, except what may be absolutely necessary for executing it’s inspection Laws.” Art. I, 

§10, cl. 2 (emphasis added). This assumed what everyone

assumed: that the States could exclude from their territory

dangerous or unwholesome goods. A later portion of the 

same section provides that “[n]o State shall, without the 

Consent of Congress, . . . engage in War, unless actually 

invaded, or in such imminent Danger as will not admit of 

delay.” Art. I, §10, cl. 3 (emphasis added). This limits the 

States’ sovereignty (in a way not relevant here) but leaves

intact their inherent power to protect their territory.

Notwithstanding “[t]he myth of an era of unrestricted 
 

 

4 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

immigration” in the first 100 years of the Republic, the

States enacted numerous laws restricting the immigration of certain classes of aliens, including convicted criminals, indigents, persons with contagious diseases, and (in 

Southern States) freed blacks. Neuman, The Lost Century 

of American Immigration (1776–1875), 93 Colum. L. Rev.

1833, 1835, 1841–1880 (1993). State laws not only provided for the removal of unwanted immigrants but also

imposed penalties on unlawfully present aliens and those 

who aided their immigration.2 Id., at 1883. 

In fact, the controversy surrounding the Alien and

Sedition Acts involved a debate over whether, under the 

Constitution, the States had exclusive authority to enact

such immigration laws. Criticism of the Sedition Act has 

become a prominent feature of our First Amendment 

jurisprudence, see, e.g., New York Times Co. v. Sullivan, 

376 U. S. 254, 273–276 (1964), but one of the Alien Acts3 

also aroused controversy at the time: 

“Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That it shall be lawful for the President of 

the United States at any time during the continuance 

of this act, to order all such aliens as he shall judge

dangerous to the peace and safety of the United

States, or shall have reasonable grounds to suspect 

are concerned in any treasonable or secret machinations against the government thereof, to depart out of

the territory of the United States . . . .” An Act concerning Aliens, 1 Stat. 570, 570–571. 

—————— 

2 E.g., Va. Code Tit. 54, ch. 198, §39 (1849) (“If a master of a vessel or

other person, knowingly, import or bring into this state, from any place 

out of the United States, any person convicted of crime . . . he shall be

confined in jail for three months, and be fined one hundred dollars”). 3There were two Alien Acts, one of which dealt only with enemy 

aliens. An Act respecting Alien Enemies, 1 Stat. 577. 
 

Cite as: 567 U. S. ____ (2012) 5 

Opinion of SCALIA, J. 

The Kentucky and Virginia Resolutions, written in denunciation of these Acts, insisted that the power to exclude

unwanted aliens rested solely in the States. Jefferson’s 

Kentucky Resolutions insisted “that alien friends are 

under the jurisdiction and protection of the laws of the

state wherein they are [and] that no power over them has 

been delegated to the United States, nor prohibited to 

the individual states, distinct from their power over citizens.” Kentucky Resolutions of 1798, reprinted in J. Powell,

Languages of Power: A Sourcebook of Early American 

Constitutional History 131 (1991). Madison’s Virginia 

Resolutions likewise contended that the Alien Act purported to give the President “a power nowhere delegated

to the federal government.” Virginia Resolutions of 1798, 

reprinted in Powell, supra, at 134 (emphasis omitted). 

Notably, moreover, the Federalist proponents of the Act

defended it primarily on the ground that “[t]he removal of 

aliens is the usual preliminary of hostility” and could 

therefore be justified in exercise of the Federal Government’s war powers. Massachussets Resolutions in Reply 

to Virginia, reprinted in Powell, supra, at 136.

 In Mayor of New York v. Miln, this Court considered 

a New York statute that required the commander of any 

ship arriving in New York from abroad to disclose “the

name, place of birth, and last legal settlement, age and 

occupation . . . of all passengers . . . with the intention of 

proceeding to the said city.” 11 Pet., at 130–131. After 

discussing the sovereign authority to regulate the entrance of foreigners described by De Vattel, the Court said: 

“The power . . . of New York to pass this law having

undeniably existed at the formation of the constitution, the simply inquiry is, whether by that instrument it was taken from the states, and granted to

congress; for if it were not, it yet remains with them.” 

Id., at 132. 
 

 

 

6 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

And the Court held that it remains. Id., at 139. 

II 

One would conclude from the foregoing that after the

adoption of the Constitution there was some doubt about 

the power of the Federal Government to control immigration, but no doubt about the power of the States to do so.

Since the founding era (though not immediately), doubt 

about the Federal Government’s power has disappeared. 

Indeed, primary responsibility for immigration policy has

shifted from the States to the Federal Government. Congress exercised its power “[t]o establish an uniform Rule of 

Naturalization,” Art. I, §8, cl. 4, very early on, see An Act 

to establish an uniform Rule of Naturalization, 1 Stat. 

103. But with the fleeting exception of the Alien Act,

Congress did not enact any legislation regulating immigration for the better part of a century. In 1862, Congress

passed “An Act to prohibit the ‘Coolie Trade’ by American

Citizens in American Vessels,” which prohibited “procuring [Chinese nationals] . . . to be disposed of, or sold, or 

transferred, for any term of years or for any time whatever, as servants or apprentices, or to be held to service or

labor.” 12 Stat. 340. Then, in 1875, Congress amended 

that act to bar admission to Chinese, Japanese, and other 

Asian immigrants who had “entered into a contract or 

agreement for a term of service within the United States, 

for lewd and immoral purposes.” An act supplementary to 

the acts in relation to immigration, ch. 141, 18 Stat. 477. 

And in 1882, Congress enacted the first general immigration statute. See An act to regulate Immigration, 22 

Stat. 214. Of course, it hardly bears mention that Federal 

immigration law is now extensive.

I accept that as a valid exercise of federal power—not

because of the Naturalization Clause (it has no necessary 

connection to citizenship) but because it is an inherent 

attribute of sovereignty no less for the United States than 
 

Cite as: 567 U. S. ____ (2012) 7 

Opinion of SCALIA, J. 

for the States. As this Court has said, it is an “‘accepted 

maxim of international law, that every sovereign nation

has the power, as inherent in sovereignty, and essential to 

self-preservation, to forbid the entrance of foreigners

within its dominions.’” Fong Yue Ting v. United States, 

149 U. S. 698, 705 (1893) (quoting Ekiu v. United States, 

142 U. S. 651, 659 (1892)). That is why there was no need 

to set forth control of immigration as one of the enumerated powers of Congress, although an acknowledgment of

that power (as well as of the States’ similar power, subject 

to federal abridgment) was contained in Art. I, §9, which

provided that “[t]he Migration or Importation of such 

Persons as any of the States now existing shall think 

proper to admit, shall not be prohibited by the Congress

prior to the Year one thousand eight hundred and 

eight . . . .”

In light of the predominance of federal immigration

restrictions in modern times, it is easy to lose sight of the

States’ traditional role in regulating immigration—and to

overlook their sovereign prerogative to do so. I accept as a

given that State regulation is excluded by the Constitution 

when (1) it has been prohibited by a valid federal law, or 

(2) it conflicts with federal regulation—when, for example, 

it admits those whom federal regulation would exclude, or

excludes those whom federal regulation would admit. 

Possibility (1) need not be considered here: there is no

federal law prohibiting the States’ sovereign power to exclude (assuming federal authority to enact such a law). 

The mere existence of federal action in the immigration 

area—and the so-called field preemption arising from that 

action, upon which the Court’s opinion so heavily relies, 

ante, at 9–11—cannot be regarded as such a prohibition.

We are not talking here about a federal law prohibiting 

the States from regulating bubble-gum advertising, or 

even the construction of nuclear plants. We are talking 

about a federal law going to the core of state sovereignty: 
 

 

 

8 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

the power to exclude. Like elimination of the States’ other 

inherent sovereign power, immunity from suit, elimination of the States’ sovereign power to exclude requires that 

“Congress . . . unequivocally expres[s] its intent to abrogate,” Seminole Tribe of Fla. v. Florida, 517 U. S. 44, 55 

(1996) (internal quotation marks and citation omitted).

Implicit “field preemption” will not do.

Nor can federal power over illegal immigration be

deemed exclusive because of what the Court’s opinion 

solicitously calls “foreign countries[’] concern[s] about the 

status, safety, and security of their nationals in the United

States,” ante, at 3. The Constitution gives all those on our

shores the protections of the Bill of Rights—but just as 

those rights are not expanded for foreign nationals because of their countries’ views (some countries, for example, have recently discovered the death penalty to be 

barbaric), neither are the fundamental sovereign powers

of the States abridged to accommodate foreign countries’ 

views. Even in its international relations, the Federal 

Government must live with the inconvenient fact that it is 

a Union of independent States, who have their own sovereign powers. This is not the first time it has found that a 

nuisance and a bother in the conduct of foreign policy.

Four years ago, for example, the Government importuned 

us to interfere with thoroughly constitutional state judicial 

procedures in the criminal trial of foreign nationals because the international community, and even an opinion of 

the International Court of Justice, disapproved them. See 

Medellín v. Texas, 552 U. S. 491 (2008). We rejected that

request, as we should reject the Executive’s invocation of 

foreign-affairs considerations here. Though it may upset

foreign powers—and even when the Federal Government

desperately wants to avoid upsetting foreign powers—the

States have the right to protect their borders against

foreign nationals, just as they have the right to execute

foreign nationals for murder. 
Cite as: 567 U. S. ____ (2012) 9 

Opinion of SCALIA, J. 

What this case comes down to, then, is whether the 

Arizona law conflicts with federal immigration law—

whether it excludes those whom federal law would admit, 

or admits those whom federal law would exclude. It does 

not purport to do so. It applies only to aliens who neither 

possess a privilege to be present under federal law nor 

have been removed pursuant to the Federal Government’s 

inherent authority. I proceed to consider the challenged 

provisions in detail. 

§2(B) 

“For any lawful stop, detention or arrest made by a 

law enforcement official . . . in the enforcement of any

other law or ordinance of a county, city or town or this 

state where reasonable suspicion exists that the person is an alien and is unlawfully present in the United 

States, a reasonable attempt shall be made, when 

practicable, to determine the immigration status of 

the person, except if the determination may hinder or

obstruct an investigation. Any person who is arrested

shall have the person’s immigration status determined before the person is released. . . .” S. B. 1070,

§2(B), as amended, Ariz. Rev. Stat. Ann. §11–1051(B) 

(West 2012). 

The Government has conceded that “even before Section 

2 was enacted, state and local officers had state-law authority to inquire of DHS [the Department of Homeland 

Security] about a suspect’s unlawful status and otherwise cooperate with federal immigration officers.” Brief for 

United States 47 (citing App. 62, 82); see also Brief for 

United States 48–49. That concession, in my view, obviates the need for further inquiry. The Government’s 

conflict-pre-emption claim calls on us “to determine 

whether, under the circumstances of this particular case, 

[the State’s] law stands as an obstacle to the accomplishment and execution of the full purposes and objectives of 
 

 

10 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

Congress.” Hines v. Davidowitz, 312 U. S. 52, 67 (1941) 

(emphasis added). It is impossible to make such a finding 

without a factual record concerning the manner in which

Arizona is implementing these provisions—something the

Government’s pre-enforcement challenge has pretermitted.

“The fact that [a law] might operate unconstitutionally 

under some conceivable set of circumstances is insufficient to render it wholly invalid, since we have not

recognized an ‘overbreadth’ doctrine outside the limited 

context of the First Amendment.” United States v. Salerno, 481 U. S. 739, 745 (1987). And on its face, §2(B)

merely tells state officials that they are authorized to do

something that they were, by the Government’s concession, already authorized to do. 

The Court therefore properly rejects the Government’s

challenge, recognizing that, “[a]t this stage, without the 

benefit of a definitive interpretation from the state courts, 

it would be inappropriate to assume §2B will be construed

in a way that creates a conflict with federal law.” Ante, at 

23. Before reaching that conclusion, however, the Court 

goes to great length to assuage fears that “state officers

will be required to delay the release of some detainees for 

no reason other than to verify their immigration status.” 

Ante, at 22. Of course, any investigatory detention, including one under §2(B), may become an “unreasonable

. . . seizur[e],” U. S. Const., Amdt. IV, if it lasts too long. 

See Illinois v. Caballes, 543 U. S. 405, 407 (2005). But 

that has nothing to do with this case, in which the Government claims that §2(B) is pre-empted by federal immigration law, not that anyone’s Fourth Amendment rights 

have been violated. And I know of no reason why a 

protracted detention that does not violate the Fourth

Amendment would contradict or conflict with any federal

immigration law. 
Cite as: 567 U. S. ____ (2012) 11 

Opinion of SCALIA, J. 

§6 

“A peace officer, without a warrant, may arrest a person if the officer has probable cause to believe . . .

[t]he person to be arrested has committed any public

offense that makes the person removable from the

United States.” S. B. 1070, §6(A)(5), Ariz. Rev. Stat.

Ann. §13–3883(A)(5) (West Supp. 2011). 

This provision of S. B. 1070 expands the statutory list of

offenses for which an Arizona police officer may make an 

arrest without a warrant. See §13–3883. If an officer has 

probable cause to believe that an individual is “removable”

by reason of a public offense, then a warrant is not required to make an arrest. The Government’s primary 

contention is that §6 is pre-empted by federal immigration

law because it allows state officials to make arrests “without regard to federal priorities.” Brief for United States 

53. The Court’s opinion focuses on limits that Congress 

has placed on federal officials’ authority to arrest removable aliens and the possibility that state officials will

make arrests “to achieve [Arizona’s] own immigration policy” 

and “without any input from the Federal Government.” 

Ante, at 17. 

Of course on this pre-enforcement record there is no 

reason to assume that Arizona officials will ignore federal 

immigration policy (unless it be the questionable policy of 

not wanting to identify illegal aliens who have committed 

offenses that make them removable). As Arizona points

out, federal law expressly provides that state officers may 

“cooperate with the Attorney General in the identification, 

apprehension, detention, or removal of aliens not lawfully 

present in the United States,” 8 U. S. C. §1357(g)(10)(B);

and “cooperation” requires neither identical efforts nor

prior federal approval. It is consistent with the Arizona 

statute, and with the “cooperat[ive]” system that Congress 

has created, for state officials to arrest a removable alien, 
 

12 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

contact federal immigration authorities, and follow their 

lead on what to do next. And it is an assault on logic to

say that identifying a removable alien and holding him for

federal determination of whether he should be removed 

“violates the principle that the removal process is entrusted

to the discretion of the Federal Government,” ante, at 

18. The State’s detention does not represent commencement of the removal process unless the Federal Government makes it so. 

But that is not the most important point. The most 

important point is that, as we have discussed, Arizona is 

entitled to have “its own immigration policy”—including a

more rigorous enforcement policy—so long as that does not 

conflict with federal law. The Court says, as though the 

point is utterly dispositive, that “it is not a crime for a 

removable alien to remain present in the United States,” 

ante, at 15. It is not a federal crime, to be sure. But there 

is no reason Arizona cannot make it a state crime for a 

removable alien (or any illegal alien, for that matter) to 

remain present in Arizona.

The Court quotes 8 U. S. C. §1226(a), which provides 

that, “[o]n a warrant issued by the Attorney General, an

alien may be arrested and detained pending a decision on 

whether the alien is to be removed from the United 

States.” Section 1357(a)(2) also provides that a federal 

immigration official “shall have power without warrant . . . 

to arrest any alien in the United States, if he has reason to

believe that the alien so arrested is in the United States in 

violation of any [federal immigration] law or regulation 

and is likely to escape before a warrant can be obtained for 

his arrest.” But statutory limitations upon the actions of 

federal officers in enforcing the United States’ power to

protect its borders do not on their face apply to the actions 

of state officers in enforcing the State’s power to protect its 

borders. There is no more reason to read these provisions 

as implying that state officials are subject to similar limi­
Cite as: 567 U. S. ____ (2012) 13 

Opinion of SCALIA, J. 

tations than there is to read them as implying that only 

federal officials may arrest removable aliens. And in any 

event neither implication would constitute the sort of clear

elimination of the States’ sovereign power that our cases 

demand. 

The Court raises concerns about “unnecessary harassment of some aliens . . . whom federal officials determine 

should not be removed.” Ante, at 17. But we have no 

license to assume, without any support in the record, that

Arizona officials would use their arrest authority under §6

to harass anyone. And it makes no difference that federal 

officials might “determine [that some unlawfully present 

aliens] should not be removed,” ibid. They may well determine not to remove from the United States aliens who 

have no right to be here; but unless and until these aliens

have been given the right to remain, Arizona is entitled to

arrest them and at least bring them to federal officials’ 

attention, which is all that §6 necessarily entails. (In my

view, the State can go further than this, and punish them

for their unlawful entry and presence in Arizona.)

The Government complains that state officials might not 

heed “federal priorities.” Indeed they might not, particularly if those priorities include willful blindness or deliberate inattention to the presence of removable aliens in 

Arizona. The State’s whole complaint—the reason this 

law was passed and this case has arisen—is that the 

citizens of Arizona believe federal priorities are too lax. 

The State has the sovereign power to protect its borders 

more rigorously if it wishes, absent any valid federal

prohibition. The Executive’s policy choice of lax federal

enforcement does not constitute such a prohibition. 

§3 

“In addition to any violation of federal law, a person is 

guilty of willful failure to complete or carry an alien

registration document if the person is in violation of 8 
 

 

14 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

[U. S. C.] §1304(e) or §1306(a).” S. B. 1070, §3(A), as 

amended, Ariz. Rev. Stat. Ann. §13–1509(A). 

It is beyond question that a State may make violation of 

federal law a violation of state law as well. We have held 

that to be so even when the interest protected is a distinctively federal interest, such as protection of the dignity of 

the national flag, see Halter v. Nebraska, 205 U. S. 34 

(1907), or protection of the Federal Government’s ability 

to recruit soldiers, Gilbert v. Minnesota, 254 U. S. 325 

(1920). “[T]he State is not inhibited from making the national

purposes its own purposes to the extent of exerting its 

police power to prevent its own citizens from obstructing

the accomplishment of such purposes.” Id., at 331 (internal quotation marks omitted). Much more is that so when, 

as here, the State is protecting its own interest, the integrity of its borders. And we have said that explicitly with 

regard to illegal immigration: “Despite the exclusive federal control of this Nation’s borders, we cannot conclude 

that the States are without any power to deter the influx

of persons entering the United States against federal law,

and whose numbers might have a discernible impact on

traditional state concerns.” Plyler v. Doe, 457 U. S. 202, 

228, n. 23 (1982). 

The Court’s opinion relies upon Hines v. Davidowitz, 

supra. Ante, at 9–10. But that case did not, as the Court 

believes, establish a “field preemption” that implicitly

eliminates the States’ sovereign power to exclude those

whom federal law excludes. It held that the States are not 

permitted to establish “additional or auxiliary” registration requirements for aliens. 312 U. S., at 66–67. But §3

does not establish additional or auxiliary registration

requirements. It merely makes a violation of state law the 

very same failure to register and failure to carry evidence

of registration that are violations of federal law. Hines 

does not prevent the State from relying on the federal 
Cite as: 567 U. S. ____ (2012) 15 

Opinion of SCALIA, J. 

registration system as “an available aid in the enforcement of a number of statutes of the state applicable to 

aliens whose constitutional validity has not been questioned.” Id., at 75–76 (Stone, J., dissenting). One such 

statute is Arizona’s law forbidding illegal aliens to collect 

unemployment benefits, Ariz. Rev. Stat. Ann. §23–781(B) 

(West 2012). To enforce that and other laws that validly 

turn on alien status, Arizona has, in Justice Stone’s words, 

an interest in knowing “the number and whereabouts of 

aliens within the state” and in having “a means of their 

identification,” 312 U. S., at 75. And it can punish the 

aliens’ failure to comply with the provisions of federal law 

that make that knowledge and identification possible.

In some areas of uniquely federal concern—e.g., fraud in 

a federal administrative process (Buckman Co. v. Plaintiffs’ Legal Comm., 531 U. S. 341 (2001)) or perjury in 

violation of a federally required oath (In re Loney, 134 

U. S. 372 (1890))—this Court has held that a State has no 

legitimate interest in enforcing a federal scheme. But the 

federal alien registration system is certainly not of uniquely

federal interest. States, private entities, and individuals 

rely on the federal registration system (including the 

E-Verify program) on a regular basis. Arizona’s legitimate interest in protecting (among other things) its unemploymentbenefits system is an entirely adequate basis for making 

the violation of federal registration and carry requirements a violation of state law as well. 

The Court points out, however, ante, at 11, that in some 

respects the state law exceeds the punishments prescribed

by federal law: It rules out probation and pardon, which

are available under federal law. The answer is that it 

makes no difference. Illegal immigrants who violate §3 

violate Arizona law. It is one thing to say that the Supremacy Clause prevents Arizona law from excluding

those whom federal law admits. It is quite something else

to say that a violation of Arizona law cannot be punished 
 

 

 

16 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

more severely than a violation of federal law. Especially

where (as here) the State is defending its own sovereign 

interests, there is no precedent for such a limitation. The 

sale of illegal drugs, for example, ordinarily violates state

law as well as federal law, and no one thinks that the 

state penalties cannot exceed the federal. As I have discussed, moreover, “field preemption” cannot establish a

prohibition of additional state penalties in the area of 

immigration.

Finally, the Government also suggests that §3 poses an 

obstacle to the administration of federal immigration law,

see Brief for United States 31–33, but “there is no conflict 

in terms, and no possibility of such conflict, [if] the state 

statute makes federal law its own,” California v. Zook, 336 

U. S. 725, 735 (1949).

It holds no fear for me, as it does for the Court, that 

“[w]ere §3 to come into force, the State would have the

power to bring criminal charges against individuals for 

violating a federal law even in circumstances where federal officials in charge of the comprehensive scheme determine that prosecution would frustrate federal policies.” 

Ante, at 11. That seems to me entirely appropriate when 

the State uses the federal law (as it must) as the criterion 

for the exercise of its own power, and the implementation 

of its own policies of excluding those who do not belong 

there. What I do fear—and what Arizona and the States 

that support it fear—is that “federal policies” of nonenforcement will leave the States helpless before those evil

effects of illegal immigration that the Court’s opinion 

dutifully recites in its prologue (ante, at 6) but leaves

unremedied in its disposition. 

§5(C) 

“It is unlawful for a person who is unlawfully present 

in the United States and who is an unauthorized alien 

to knowingly apply for work, solicit work in a public 
Cite as: 567 U. S. ____ (2012) 17 

Opinion of SCALIA, J. 

place or perform work as an employee or independent

contractor in this state.” S. B. 1070, §5(C), as amended,

Ariz. Rev. Stat. Ann. §13–2928(C). 

Here, the Court rightly starts with De Canas v. Bica, 

424 U. S. 351 (1976), which involved a California law 

providing that “‘[n]o employer shall knowingly employ an

alien who is not entitled to lawful residence in the United 

States if such employment would have an adverse effect 

on lawful resident workers.’” Id., at 352 (quoting California Labor Code Ann. §2805(a)). This Court concluded that 

the California law was not pre-empted, as Congress had 

neither occupied the field of “regulation of employment of

illegal aliens” nor expressed “the clear and manifest purpose” of displacing such state regulation. Id., at 356–357 

(internal quotation marks omitted). Thus, at the time 

De Canas was decided, §5(C) would have been indubitably 

lawful. 

The only relevant change is that Congress has since

enacted its own restrictions on employers who hire illegal 

aliens, 8 U. S. C. §1324a, in legislation that also includes 

some civil (but no criminal) penalties on illegal aliens who

accept unlawful employment. The Court concludes from 

this (reasonably enough) “that Congress made a deliberate 

choice not to impose criminal penalties on aliens who seek,

or engage in, unauthorized employment,” ante, at 13. But 

that is not the same as a deliberate choice to prohibit

the States from imposing criminal penalties. Congress’s

intent with regard to exclusion of state law need not be 

guessed at, but is found in the law’s express pre-emption

provision, which excludes “any State or local law imposing civil or criminal sanctions (other than through licensing and similar laws) upon those who employ, or recruit 

or refer for a fee for employment, unauthorized aliens,” 

§1324a(h)(2) (emphasis added). Common sense, reflected 

in the canon expressio unius est exclusio alterius, suggests 
 

18 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

that the specification of pre-emption for laws punishing

“those who employ” implies the lack of pre-emption for 

other laws, including laws punishing “those who seek or

accept employment.”

The Court has no credible response to this. It quotes

our jurisprudence to the effect that an “express preemption provisio[n] does not bar the ordinary working of

conflict pre-emption principles.” Ante, at 14 (quoting Geier 

v. American Honda Motor Co., 529 U. S. 861, 869 

(2000) (internal quotation marks omitted)). True enough— 

conflict preemption principles. It then goes on say that

since “Congress decided it would be inappropriate to impose criminal penalties on aliens who seek or engage in 

unauthorized employment,” “[i]t follows that a state law to

the contrary is an obstacle to the regulatory system Congress chose.” Ante, at 15. For “‘[w]here a comprehensive

federal scheme intentionally leaves a portion of the regulated field without controls, then the pre-emptive inference

can be drawn.’” Ibid. (quoting Puerto Rico Dept. of Consumer Affairs v. ISLA Petroleum Corp., 485 U.S. 495, 503 

(1988)). All that is a classic description not of conflict 

pre-emption but of field pre-emption, which (concededly)

does not occur beyond the terms of an express pre-emption 

provision.

The Court concludes that §5(C) “would interfere with 

the careful balance struck by Congress,” ante, at 15, (another field pre-emption notion, by the way) but that is easy 

to say and impossible to demonstrate. The Court relies 

primarily on the fact that “[p]roposals to make unauthorized work a criminal offense were debated and discussed 

during the long process of drafting [the Immigration Reform and Control Act of 1986 (IRCA)],” “[b]ut Congress 

rejected them.” Ante, at 14. There is no more reason to 

believe that this rejection was expressive of a desire that 

there be no sanctions on employees, than expressive of a 

desire that such sanctions be left to the States. To tell the 
 

Cite as: 567 U. S. ____ (2012) 19 

Opinion of SCALIA, J. 

truth, it was most likely expressive of what inaction ordinarily expresses: nothing at all. It is a “naïve assumption

that the failure of a bill to make it out of committee, or 

to be adopted when reported to the floor, is the same

as a congressional rejection of what the bill contained.” 

Crosby v. National Foreign Trade Council, 530 U. S. 363, 

389 (2000) (SCALIA, J., concurring in judgment) (internal

quotation marks and alterations omitted). 

* * * 

The brief for the Government in this case asserted that 

“the Executive Branch’s ability to exercise discretion and 

set priorities is particularly important because of the need

to allocate scarce enforcement resources wisely.” Brief for 

United States 21. Of course there is no reason why the

Federal Executive’s need to allocate its scarce enforcement 

resources should disable Arizona from devoting its resources to illegal immigration in Arizona that in its view 

the Federal Executive has given short shrift. Despite

Congress’s prescription that “the immigration laws of the

United States should be enforced vigorously and uniformly,” 

IRCA §115, 100 Stat. 3384, Arizona asserts without 

contradiction and with supporting citations: 

“[I]n the last decade federal enforcement efforts have

focused primarily on areas in California and Texas, 

leaving Arizona’s border to suffer from comparative

neglect. The result has been the funneling of an increasing tide of illegal border crossings into Arizona. 

Indeed, over the past decade, over a third of the Nation’s illegal border crossings occurred in Arizona.” 

Brief for Petitioners 2–3 (footnote omitted). 

Must Arizona’s ability to protect its borders yield to the

reality that Congress has provided inadequate funding for 

federal enforcement—or, even worse, to the Executive’s 

unwise targeting of that funding? 
 

20 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

But leave that aside. It has become clear that federal 

enforcement priorities—in the sense of priorities based on 

the need to allocate “scarce enforcement resources”—is not 

the problem here. After this case was argued and while 

it was under consideration, the Secretary of Homeland

Security announced a program exempting from immigration enforcement some 1.4 million illegal immigrants 

under the age of 30.4 If an individual unlawfully present

in the United States 

“• came to the United States under the age of sixteen; 

“• has continuously resided in the United States for 

at least five years . . . , 

“• is currently in school, has graduated from high

school, has obtained a general education development certificate, or is an honorably discharged 

veteran . . . , 

“• has not been convicted of a [serious crime]; and 

“• is not above the age of thirty,”5 

then U. S. immigration officials have been directed to 

“defe[r] action” against such individual “for a period of two 

years, subject to renewal.”6 The husbanding of scarce

enforcement resources can hardly be the justification for 

this, since the considerable administrative cost of conducting as many as 1.4 million background checks, and ruling

on the biennial requests for dispensation that the nonen­

—————— 

4Preston & Cushman, Obama to Permit Young Migrants to Remain 

in U. S., N. Y. Times, June 16, 2012, p. A1. 5Memorandum from Janet Napolitano, Secretary of Homeland Security, to David V. Aguilar, Acting Commissioner, U. S. Customs and 

Border Protection; Alejandro Mayorkas, Director, U. S. Citizenship 

and Immigration Services; and John Morton, Director, U. S. Immigration and Customs Enforcement, p. 1 (June 15, 2012), online at

http://www.dhs.gov (all Internet materials as visited June 22, 2012, and 

available in Clerk of Court’s case file). 6 Id., at 2. 
 

Cite as: 567 U. S. ____ (2012) 21 

Opinion of SCALIA, J. 

forcement program envisions, will necessarily be deducted 

from immigration enforcement. The President said at a 

news conference that the new program is “the right thing

to do” in light of Congress’s failure to pass the Administration’s proposed revision of the Immigration Act.7 Perhaps

it is, though Arizona may not think so. But to say, as the 

Court does, that Arizona contradicts federal law by enforcing applications of the Immigration Act that the President 

declines to enforce boggles the mind. 

The Court opinion’s looming specter of inutterable horror—“[i]f §3 of the Arizona statute were valid, every State

could give itself independent authority to prosecute federal registration violations,” ante, at 10—seems to me not 

so horrible and even less looming. But there has come to 

pass, and is with us today, the specter that Arizona and 

the States that support it predicted: A Federal Government that does not want to enforce the immigration laws

as written, and leaves the States’ borders unprotected 

against immigrants whom those laws would exclude. So 

the issue is a stark one. Are the sovereign States at the

mercy of the Federal Executive’s refusal to enforce the 

Nation’s immigration laws?

A good way of answering that question is to ask: Would 

the States conceivably have entered into the Union if the

Constitution itself contained the Court’s holding? Today’s

judgment surely fails that test. At the Constitutional 

Convention of 1787, the delegates contended with “the 

jealousy of the states with regard to their sovereignty.” 1

Records of the Federal Convention 19 (M. Farrand ed.

1911) (statement of Edmund Randolph). Through ratification of the fundamental charter that the Convention produced, the States ceded much of their sovereignty to the 

Federal Government. But much of it remained jealously 

—————— 

7Remarks by the President on Immigration (June 15, 2012), online at

http://www.whitehouse.gov. 
 

22 ARIZONA v. UNITED STATES 

Opinion of SCALIA, J. 

guarded—as reflected in the innumerable proposals that

never left Independence Hall. Now, imagine a provision—

perhaps inserted right after Art. I, §8, cl. 4, the Naturalization Clause—which included among the enumerated 

powers of Congress “To establish Limitations upon Immigration that will be exclusive and that will be enforced 

only to the extent the President deems appropriate.” The 

delegates to the Grand Convention would have rushed to 

the exits. 

As is often the case, discussion of the dry legalities that 

are the proper object of our attention suppresses the very

human realities that gave rise to the suit. Arizona bears 

the brunt of the country’s illegal immigration problem. Its 

citizens feel themselves under siege by large numbers of 

illegal immigrants who invade their property, strain their 

social services, and even place their lives in jeopardy. 

Federal officials have been unable to remedy the problem,

and indeed have recently shown that they are unwilling to 

do so. Thousands of Arizona’s estimated 400,000 illegal 

immigrants—including not just children but men and 

women under 30—are now assured immunity from enforcement, and will be able to compete openly with Arizona citizens for employment.

Arizona has moved to protect its sovereignty—not in

contradiction of federal law, but in complete compliance

with it. The laws under challenge here do not extend or

revise federal immigration restrictions, but merely enforce 

those restrictions more effectively. If securing its territory

in this fashion is not within the power of Arizona, we 

should cease referring to it as a sovereign State. I dissent. 
_________________ 

_________________ 


 


 

Cite as: 567 U. S. ____ (2012) 1 

Opinion of THOMAS, J. 

SUPREME COURT OF THE UNITED STATES 

No. 11–182 

ARIZONA, ET AL., PETITIONERS v. UNITED STATES 

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
 

APPEALS FOR THE NINTH CIRCUIT
 

[June 25, 2012] 

JUSTICE THOMAS, concurring in part and dissenting in 

part. 

I agree with JUSTICE SCALIA that federal immigration

law does not pre-empt any of the challenged provisions of

S. B. 1070. I reach that conclusion, however, for the simple reason that there is no conflict between the “ordinary

meanin[g]” of the relevant federal laws and that of the

four provisions of Arizona law at issue here. Wyeth v. 

Levine, 555 U. S. 555, 588 (2009) (THOMAS, J., concurring

in judgment) (“Pre-emption analysis should not be a freewheeling judicial inquiry into whether a state statute is in 

tension with federal objectives, but an inquiry into whether 

the ordinary meanings of state and federal law conflict” 

(brackets; internal quotation marks omitted)). 

Section 2(B) of S. B. 1070 provides that, when Arizona

law enforcement officers reasonably suspect that a person

they have lawfully stopped, detained, or arrested is unlawfully present, “a reasonable attempt shall be made, when 

practicable, to determine the immigration status of the 

person” pursuant to the verification procedure established 

by Congress in 8 U. S. C. §1373(c). Ariz. Rev. Stat. Ann. 

§11–1051(B) (West 2012). Nothing in the text of that or

any other federal statute prohibits Arizona from directing 

its officers to make immigration-related inquiries in these

situations. To the contrary, federal law expressly states 

that “no State or local government entity may be prohib- 
 

 

2 ARIZONA v. UNITED STATES 

Opinion of THOMAS, J. 

ited, or in any way restricted, from sending to or receiving

from” federal officials “information regarding the immigration status” of an alien. 8 U. S. C. §1644. And, federal 

law imposes an affirmative obligation on federal officials 

to respond to a State’s immigration-related inquiries.

§1373(c).

Section 6 of S. B. 1070 authorizes Arizona law enforcement officers to make warrantless arrests when there is 

probable cause to believe that an arrestee has committed a

public offense that renders him removable under federal 

immigration law. States, as sovereigns, have inherent 

authority to conduct arrests for violations of federal law, 

unless and until Congress removes that authority. See 

United States v. Di Re, 332 U. S. 581, 589 (1948) (holding

that state law determines the validity of a warrantless

arrest for a violation of federal law “in the absence of 

an applicable federal statute”). Here, no federal statute 

purports to withdraw that authority. As JUSTICE SCALIA 

notes, ante, at 12 (opinion concurring in part and dissenting in part), federal law does limit the authority of federal 

officials to arrest removable aliens, but those statutes do 

not apply to state officers. And, federal law expressly

recognizes that state officers may “cooperate with the 

Attorney General” in the “apprehension” and “detention”

of “aliens not lawfully present in the United States.” 

§1357(g)(10)(B). Nothing in that statute indicates that

such cooperation requires a prior “request, approval, or 

other instruction from the Federal Government.” Ante, at 

18 (majority opinion).

Section 3 of S. B. 1070 makes it a crime under Arizona 

law for an unlawfully present alien to willfully fail to 

complete or carry an alien registration document in violation of 8 U. S. C. §1304(e) and §1306(a). Section 3 simply

incorporates federal registration standards. Unlike the 

Court, I would not hold that Congress pre-empted the field 

of enforcing those standards. “[O]ur recent cases have 
 

Cite as: 567 U. S. ____ (2012) 3 

Opinion of THOMAS, J. 

frequently rejected field pre-emption in the absence of 

statutory language expressly requiring it.” Camps Newfound/Owatonna, Inc. v. Town of Harrison, 520 U. S. 564, 

617 (1997) (THOMAS, J., dissenting); see, e.g., New York 

State Dept. of Social Servs. v. Dublino, 413 U. S. 405, 415 

(1973). Here, nothing in the text of the relevant federal 

statutes indicates that Congress intended enforcement of 

its registration requirements to be exclusively the province of the Federal Government. That Congress created a

“full set of standards governing alien registration,” ante, at 

10 (majority opinion), merely indicates that it intended the

scheme to be capable of working on its own, not that it 

wanted to preclude the States from enforcing the federal 

standards. Hines v. Davidowitz, 312 U. S. 52 (1941), is not 

to the contrary. As JUSTICE SCALIA explains, ante, at 14, 

Hines at most holds that federal law pre-empts the States 

from creating additional registration requirements. But 

here, Arizona is merely seeking to enforce the very registration requirements that Congress created. 

Section 5(C) of S. B. 1070 prohibits unlawfully present 

aliens from knowingly applying for, soliciting, or performing work in Arizona. Section 5(C) operates only on individuals whom Congress has already declared ineligible to

work in the United States. Nothing in the text of the

federal immigration laws prohibits States from imposing

their own criminal penalties on such individuals. Federal law expressly pre-empts States from “imposing civil or

criminal sanctions (other than through licensing and 

similar laws) upon those who employ, or recruit or refer 

for a fee for employment, unauthorized aliens.” 8 U. S. C. 

§1324a(h)(2) (emphasis added). But it leaves States free 

to impose criminal sanctions on the employees themselves.

Despite the lack of any conflict between the ordinary

meaning of the Arizona law and that of the federal laws at 

issue here, the Court holds that various provisions of the 

Arizona law are pre-empted because they “stan[d] as an 
 

 

 

4 ARIZONA v. UNITED STATES 

Opinion of THOMAS, J. 

obstacle to the accomplishment and execution of the full

purposes and objectives of Congress.” Hines, supra, at 67. 

I have explained that the “purposes and objectives” theory 

of implied pre-emption is inconsistent with the Constitution because it invites courts to engage in freewheeling

speculation about congressional purpose that roams well 

beyond statutory text. See Wyeth, 555 U. S., at 604 (opinion concurring in judgment); see also Williamson v. Mazda 

Motor of America, Inc., 562 U. S. ___, ___–___ (2011) (opinion concurring in judgment) (slip op., at 2–3); Haywood v. 

Drown, 556 U. S. 729, 767 (2009) (dissenting opinion). 

Under the Supremacy Clause, pre-emptive effect is to be 

given to congressionally enacted laws, not to judicially 

divined legislative purposes. See Wyeth, supra, at 604 

(THOMAS, J., concurring in judgment). Thus, even assuming the existence of some tension between Arizona’s law 

and the supposed “purposes and objectives” of Congress, I

would not hold that any of the provisions of the Arizona 

law at issue here are pre-empted on that basis. 
_________________ 

_________________ 


 


 

Cite as: 567 U. S. ____ (2012) 1 

Opinion of ALITO, J. 

SUPREME COURT OF THE UNITED STATES 

No. 11–182 

ARIZONA, ET AL., PETITIONERS v. UNITED STATES 

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
 

APPEALS FOR THE NINTH CIRCUIT
 

[June 25, 2012] 

JUSTICE ALITO, concurring in part and dissenting in 

part. 

This case concerns four provisions of Arizona’s Support 

Our Law Enforcement and Safe Neighborhoods Act, S. B.

1070. Section 2(B) requires Arizona law enforcement 

officers to make a “reasonable attempt,” “when practicable,” to ascertain the immigration status of any person

whom an officer lawfully stops, detains, or arrests “where

reasonable suspicion exists that the person is an alien and 

is unlawfully present in the United States.” Ariz. Rev. 

Stat. Ann. §11–1051(B) (West 2012). Section 3 provides

that an alien who willfully fails “to complete or carry an 

alien registration document” in violation of 8 U. S. C. 

§1304(e) or §1306(a) is guilty of a misdemeanor. Ariz. Rev. 

Stat. Ann. §13–1509(A) (West Supp. 2011). Section 5(C)

makes it a misdemeanor for an unauthorized alien who 

is unlawfully present in the United States “to knowingly 

apply for work, solicit work in a public place or perform

work as an employee or independent contractor.” Ariz. 

Rev. Stat. Ann. §13–2928(C). And §6 authorizes Arizona

law enforcement officers to arrest without a warrant any

person who an officer has probable cause to believe “has

committed any public offense that makes the person removable from the United States.” Ariz. Rev. Stat. Ann. 

§13–3883(A)(5).

I agree with the Court that §2(B) is not pre-empted. 
 

2 ARIZONA v. UNITED STATES 

Opinion of ALITO, J. 

That provision does not authorize or require Arizona law 

enforcement officers to do anything they are not already 

allowed to do under existing federal law. The United 

States’ argument that §2(B) is pre-empted, not by any

federal statute or regulation, but simply by the Executive’s

current enforcement policy is an astounding assertion of

federal executive power that the Court rightly rejects. 

I also agree with the Court that §3 is pre-empted by

virtue of our decision in Hines v. Davidowitz, 312 U. S. 

52 (1941). Our conclusion in that case that Congress had 

enacted an “all-embracing system” of alien registration

and that States cannot “enforce additional or auxiliary 

regulations,” id., at 66–67, 74, forecloses Arizona’s attempt

here to impose additional, state-law penalties for violations of the federal registration scheme. 

While I agree with the Court on §2(B) and §3, I part

ways on §5(C) and §6. The Court’s holding on §5(C) is 

inconsistent with De Canas v. Bica, 424 U. S. 351 (1976),

which held that employment regulation, even of aliens

unlawfully present in the country, is an area of traditional 

state concern. Because state police powers are implicated 

here, our precedents require us to presume that federal

law does not displace state law unless Congress’ intent to 

do so is clear and manifest. I do not believe Congress has

spoken with the requisite clarity to justify invalidation of

§5(C). Nor do I believe that §6 is invalid. Like §2(B), §6

adds virtually nothing to the authority that Arizona law 

enforcement officers already exercise. And whatever little 

authority they have gained is consistent with federal law. 

Section 2(B)

A 

Although §2(B) of the Arizona law has occasioned much

controversy, it adds nothing to the authority that Arizona

law enforcement officers, like officers in all other States, 

already possess under federal law. For that reason, I 
Cite as: 567 U. S. ____ (2012) 3 

Opinion of ALITO, J. 

agree with the Court that §2(B) is not pre-empted.

Section 2(B) quite clearly does not expand the authority 

of Arizona officers to make stops or arrests. It is triggered

only when a “lawful stop, detention or arrest [is] made . . . 

in the enforcement of any other [state or local] law or 

ordinance.” Ariz. Rev. Stat. Ann. §11–1051(B) (emphasis 

added). Section 2(B) thus comes into play only when 

an officer has reasonable suspicion or probable cause to 

believe that a person has committed a nonimmigration 

offense. Arizona officers plainly possessed this authority 

before §2(B) took effect. 

Section 2(B) also does not expand the authority of Arizona officers to inquire about the immigration status of

persons who are lawfully detained. When a person is 

stopped or arrested and “reasonable suspicion exists that

the person is an alien and is unlawfully present in the

United States,” §2(B) instructs Arizona officers to make a 

“reasonable attempt,” “when practicable,” to ascertain that 

person’s immigration status. Ariz. Rev. Stat. Ann. §11– 

1051(B). Even before the Arizona Legislature enacted 

§2(B), federal law permitted state and local officers to

make such inquiries. In 8 U. S. C. §1357(g)(10)(A), Congress has made clear that state and local governments 

need not enter into formal agreements with the Federal

Government in order “to communicate with the [Federal

Government] regarding the immigration status of any 

individual.” In addition, Congress has mandated that

neither the Federal Government nor any state or local

government may “prohibit, or in any way restrict, any 

government entity or official from sending to, or receiving

from, [the Federal Government] information regarding the

citizenship or immigration status, lawful or unlawful, of 

any individual.” §1373(a); see also §1644 (providing that 

“no State or local government entity may be prohibited,

or in any way restricted, from sending to or receiving

from [the Federal Government] information regarding the 
 

4 ARIZONA v. UNITED STATES 

Opinion of ALITO, J. 

immigration status, lawful or unlawful, of an alien in the 

United States”). And while these provisions preserve the 

authority of state and local officers to seek immigrationstatus information from the Federal Government, another 

federal statute, §1373(c), requires that the Federal Government respond to any such inquiries “by providing the 

requested verification or status information.” It comes 

as no surprise, therefore, that many States and localities

permit their law enforcement officers to make the kinds of

inquiries that §2(B) prescribes. See App. 294–298 (reporting that officers in 59 surveyed state and local jurisdictions “generally” ask arrestees about their immigration

status while 34 do not and that officers in 78 jurisdictions 

“generally” inform Immigration and Customs Enforcement 

(ICE) when they believe an arrestee to be an undocumented 

alien while only 17 do not). Congress has invited state

and local governments to make immigration-related inquiries and has even obligated the Federal Government to

respond. Through §2(B), Arizona has taken Congress up

on that invitation. 

The United States does not deny that officers may, at 

their own discretion, inquire about the immigration status

of persons whom they lawfully detain. Instead, the United 

States argues that §2(B) is pre-empted because it impedes 

federal-state cooperation by mandating that officers verify

the immigration status of every detained person if there is 

reason to believe that the person is unlawfully present in

the country. The United States claims that §2(B)’s mandate runs contrary to federal law in that it “precludes

officers from taking [the Federal Government’s] priorities

and discretion into account.” Brief for United States 

50. “[B]y interposing a mandatory state law between state

and local officers and their federal counterparts,” writes

the United States, §2(B) “stands as an obstacle to the accomplishment of the federal requirement of cooperation 

and the full effectuation of the enforcement judgment and 
 

Cite as: 567 U. S. ____ (2012) 5 

Opinion of ALITO, J. 

discretion Congress has vested in the Executive Branch.” 

Ibid. (internal quotation marks and citation omitted). 

The underlying premise of the United States’ argument 

seems to be that state and local officers, when left to their 

own devices, generally take federal enforcement priorities 

into account. But there is no reason to think that this 

premise is true. And even if it were, it would not follow 

that §2(B)’s blanket mandate is at odds with federal law.

Nothing in the relevant federal statutes requires state and 

local officers to consider the Federal Government’s priorities before requesting verification of a person’s immigration status. Neither 8 U. S. C. §1357(g)(10) nor §1373(a) 

conditions the right of state and local officers to communicate with the Federal Government on their first taking

account of its priorities. Nor does §1373(c) condition the 

Federal Government’s obligation to answer requests for information on the sensitivity of state and local officers to 

its enforcement discretion. In fact, §1373(c) dictates that 

the Federal Government “shall respond” to any inquiry 

seeking verification of immigration status, and that command applies whether or not the requesting officer has

bothered to consider federal priorities. Because no federal 

statute requires such consideration, §2(B) does not conflict 

with federal law. 

In any event, it is hard to see how state and local officers could proceed in conformity with the Federal Government’s enforcement priorities without making an inquiry 

into a suspected alien’s immigration status. For example,

one of the Federal Government’s highest priorities is the 

apprehension and removal of aliens who have failed to

comply with a final order of removal. See App. 108. How 

can an officer identify those persons without first inquiring about their status? At bottom, the discretion 

that ultimately matters is not whether to verify a person’s 

immigration status but whether to act once the person’s

status is known. For that reason, §2(B)’s verification 
 

 

 

6 ARIZONA v. UNITED STATES 

Opinion of ALITO, J. 

requirement is not contrary to federal law because the

Federal Government retains the discretion that matters 

most––that is, the discretion to enforce the law in particular cases. If an Arizona officer contacts the Federal 

Government to verify a person’s immigration status and 

federal records reveal that the person is in the country unlawfully, the Federal Government decides, presumably based on its enforcement priorities, whether to have

the person released or transferred to federal custody.

Enforcement discretion thus lies with the Federal Government, not with Arizona. Nothing in §2(B) suggests

otherwise. 

The United States’ attack on §2(B) is quite remarkable.

The United States suggests that a state law may be preempted, not because it conflicts with a federal statute or 

regulation, but because it is inconsistent with a federal 

agency’s current enforcement priorities. Those priorities,

however, are not law. They are nothing more than agency 

policy. I am aware of no decision of this Court recognizing

that mere policy can have pre-emptive force. Cf. Barclays 

Bank PLC v. Franchise Tax Bd. of Cal., 512 U. S. 298, 330 

(1994) (holding that “Executive Branch communications

that express federal policy but lack the force of law cannot 

render unconstitutional” an “otherwise valid, congressionally condoned” state law). If §2(B) were pre-empted at

the present time because it is out of sync with the Federal 

Government’s current priorities, would it be unpre-empted 

at some time in the future if the agency’s priorities 

changed?

Like most law enforcement agencies, ICE does not set 

out inflexible rules for its officers to follow. To the contrary, it provides a list of factors to guide its officers’ 

enforcement discretion on a case-by-case basis. See Memorandum from John Morton, Director, ICE, to All Field 

Office Directors et al., p. 4 (June 17, 2011) (“This list is not 

exhaustive and no one factor is determinative. ICE offi-
 

 

Cite as: 567 U. S. ____ (2012) 7 

Opinion of ALITO, J. 

cers, agents, and attorneys should always consider prosecutorial discretion on a case-by-case basis. The decisions 

should be based on the totality of the circumstances, with

the goal of conforming to ICE’s enforcement priorities”).

Among those factors is “the agency’s civil immigration 

enforcement priorities,” ibid., which change from administration to administration. If accepted, the United States’ 

pre-emption argument would give the Executive unprecedented power to invalidate state laws that do not meet 

with its approval, even if the state laws are otherwise

consistent with federal statutes and duly promulgated

regulations. This argument, to say the least, is fundamentally at odds with our federal system. 

B 

It has been suggested that §2(B) will cause some persons who are lawfully stopped to be detained in violation 

of their constitutional rights while a prolonged investigation of their immigration status is undertaken. But nothing on the face of the law suggests that it will be enforced 

in a way that violates the Fourth Amendment or any other 

provision of the Constitution. The law instructs officers to 

make a “reasonable attempt” to investigate immigration

status, and this language is best understood as incorporating the Fourth Amendment’s standard of reasonableness.

Indeed, the Arizona Legislature has directed that §2(B)

“shall be implemented in a manner consistent with federal 

laws . . . protecting the civil rights of all persons and respecting the privileges and immunities of United States

citizens.” Ariz. Rev. Stat. Ann. §11–1051(L).

In the situations that seem most likely to occur, enforcement of §2(B) will present familiar Fourth Amendment questions. To take a common situation, suppose that

a car is stopped for speeding, a nonimmigration offense.

(Recall that §2(B) comes into play only where a stop or 

arrest is made for a nonimmigration offense.) Suppose 
 

8 ARIZONA v. UNITED STATES 

Opinion of ALITO, J. 

also that the officer who makes the stop subsequently 

acquires reasonable suspicion to believe that the driver 

entered the country illegally, which is a federal crime. See 

8 U. S. C. §1325(a).

It is well established that state and local officers generally have authority to make stops and arrests for violations of federal criminal laws. See, e.g., Miller v. United 

States, 357 U. S. 301, 305 (1958); United States v. Di Re, 

332 U. S. 581, 589 (1948). I see no reason why this principle should not apply to immigration crimes as well. Lower 

courts have so held. See, e.g., Estrada v. Rhode Island, 

594 F. 3d 56, 65 (CA1 2010) (upholding the lawfulness of 

a detention because the officer had an objectively reasonable belief that the arrestees “had committed immigration violations”); United States v. Vasquez-Alvarez, 176 

F. 3d 1294, 1296 (CA10 1999) (noting that “state lawenforcement officers have the general authority to investigate and make arrests for violations of federal immigration laws”); Gonzales v. Peoria, 722 F. 2d 468, 475 (CA9

1983), overruled on other grounds, Hodgers-Durgin v. de 

la Vina, 199 F. 3d 1037 (1999) (en banc) (holding that 

“federal law does not preclude local enforcement of the

criminal provisions” of federal immigration law). And the 

United States, consistent with the position long taken by

the Office of Legal Counsel (OLC) in the Department of

Justice, does not contend otherwise. See Brief for United 

States 55, n. 33; see also Memorandum from OLC to the 

Attorney General (Apr. 3, 2002), App. 268–273; Assistance 

by State and Local Police in Apprehending Illegal Aliens, 

20 Op. Off. Legal Counsel 26 (1996). 

More importantly, no federal statute casts doubt on this

authority. To be sure, there are a handful of statutes that 

purport to authorize state and local officers to make immigration-related arrests in certain situations. See, e.g., 8 

U. S. C. §1103(a)(10) (providing for the extension of “any” 

immigration enforcement authority to state and local 
 

Cite as: 567 U. S. ____ (2012) 9 

Opinion of ALITO, J. 

officers in the event of an “actual or imminent mass influx of aliens arriving off the coast”); §1252c(a) (providing authority to arrest criminal aliens who had illegally 

reentered the country but only after consultation with 

the Federal Government); §1324(c) (providing authority 

to make arrests for transporting and harboring certain 

aliens). But a grant of federal arrest authority in some

cases does not manifest a clear congressional intent to

displace the States’ police powers in all other cases. Without more, such an inference is too weak to overcome our 

presumption against pre-emption where traditional state 

police powers are at stake. Accordingly, in our hypothetical case, the Arizona officer may arrest the driver for 

violating §1325(a) if the officer has probable cause. And if 

the officer has reasonable suspicion, the officer may detain

the driver, to the extent permitted by the Fourth Amendment, while the question of illegal entry is investigated. 

We have held that a detention based on reasonable 

suspicion that the detainee committed a particular crime 

“can become unlawful if it is prolonged beyond the time

reasonably required to complete that mission.” Illinois v. 

Caballes, 543 U. S. 405, 407 (2005). But if during the 

course of a stop an officer acquires suspicion that a detainee committed a different crime, the detention may be 

extended for a reasonable time to verify or dispel that

suspicion. Cf. Muehler v. Mena, 544 U. S. 93, 101 (2005) 

(holding that “no additional Fourth Amendment justification” was required because any questioning concerning 

immigration status did not prolong the detention). In our 

hypothetical case, therefore, if the officer, after initially

stopping the car for speeding, has a reasonable suspicion 

that the driver entered the country illegally, the officer 

may investigate for evidence of illegal entry. But the 

length and nature of this investigation must remain within the limits set out in our Fourth Amendment cases. An 

investigative stop, if prolonged, can become an arrest and 
 

10 ARIZONA v. UNITED STATES 

Opinion of ALITO, J. 

thus require probable cause. See Caballes, supra, at 407. 

Similarly, if a person is moved from the site of the stop,

probable cause will likely be required. See Hayes v. Florida, 

470 U. S. 811, 816 (1985) (holding that the line between detention and arrest is crossed “when the police, 

without probable cause or a warrant, forcibly remove a

person from his home or other place in which he is entitled 

to be and transport him to the police station, where he is 

detained, although briefly, for investigative purposes”). 

If properly implemented, §2(B) should not lead to federal constitutional violations, but there is no denying that

enforcement of §2(B) will multiply the occasions on which 

sensitive Fourth Amendment issues will crop up. These 

civil-liberty concerns, I take it, are at the heart of most

objections to §2(B). Close and difficult questions will inevitably arise as to whether an officer had reasonable 

suspicion to believe that a person who is stopped for some

other reason entered the country illegally, and there is a 

risk that citizens, lawful permanent residents, and others 

who are lawfully present in the country will be detained. 

To mitigate this risk, Arizona could issue guidance to

officers detailing the circumstances that typically give 

rise to reasonable suspicion of unlawful presence. And in 

the spirit of the federal-state cooperation that the United

States champions, the Federal Government could share its

own guidelines. Arizona could also provide officers with a 

nonexclusive list containing forms of identification sufficient under §2(B) to dispel any suspicion of unlawful 

presence. If Arizona accepts licenses from most States as

proof of legal status, the problem of roadside detentions

will be greatly mitigated.1 

—————— 

1When the Real ID Act takes effect, the Federal Government will no 

longer accept state forms of identification that fail to meet certain 

federal requirements. §202(a)(1), 119 Stat. 312. One requirement is

that any identification be issued only on proof that the applicant 

is lawfully present in the United States. §202(c)(2)(B), id., at 313. I 
Cite as: 567 U. S. ____ (2012) 11 

Opinion of ALITO, J. 

Section 3 

I agree that §3 is pre-empted because, like the Court, I 

read the opinion in Hines to require that result. Although

there is some ambiguity in Hines, the Court largely spoke

in the language of field pre-emption. The Court explained 

that where Congress “has enacted a complete scheme of

regulation and has therein provided a standard for the

registration of aliens, states cannot, inconsistently with

the purpose of Congress, conflict or interfere with, curtail

or complement, the federal law, or enforce additional or

auxiliary regulations.” 312 U. S., at 66–67. In finding the 

Pennsylvania alien-registration law pre-empted, the Court 

observed that Congress had “provided a standard for 

alien registration in a single integrated and all-embracing 

system” and that its intent was “to protect the personal

liberties of law-abiding aliens through one uniform national registration system.” Id., at 74. If we credit our 

holding in Hines that Congress has enacted “a single integrated and all-embracing system” of alien registration

and that States cannot “complement” that system or “enforce additional or auxiliary regulations,” id., at 66–67, 74, 

then Arizona’s attempt to impose additional, state-law 

penalties for violations of federal registration requirements must be invalidated. 

Section 5(C) 

While I agree that §3 is pre-empted, I disagree with the

Court’s decision to strike down §5(C). I do so in large 

measure because the Court fails to give the same solicitude to our decision in De Canas, 424 U. S. 351, as it is 

willing to give our decision in Hines. In De Canas, the 

Court upheld against a pre-emption challenge a state law 

imposing fines on employers that hired aliens who were 

—————— 

anticipate that most, if not all, States will eventually issue forms of

identification that suffice to establish lawful presence under §2(B). 
 

 

12 ARIZONA v. UNITED STATES 

Opinion of ALITO, J. 

unlawfully present in the United States. The Court explained that the mere fact that “aliens are the subject of a

state statute does not render it a regulation of immigration.” 424 U. S., at 355. The Court emphasized instead 

that “States possess broad authority under their police 

powers to regulate the employment relationship to protect

workers within the State.” Id., at 356. In light of that

broad authority, the Court declared that “[o]nly a demonstration that complete ouster of state power . . . was ‘the

clear and manifest purpose of Congress’ would justify” the 

conclusion that “state regulation designed to protect vital

state interests must give way to paramount federal legislation.” Id., at 357 (some internal quotation marks omitted); see also Bates v. Dow Agrosciences LLC, 544 U. S. 

431, 449 (2005) (“In areas of traditional state regulation,

[the Court] assume[s] that a federal statute has not supplanted state law unless Congress has made such an

intention ‘clear and manifest’” (some internal quotation 

marks omitted)). 

The Court now tells us that times have changed. Since 

De Canas, Congress has enacted “a comprehensive framework for combating the employment of illegal aliens,” and 

even though aliens who seek or obtain unauthorized work 

are not subject to criminal sanctions, they can suffer civil 

penalties. Ante, at 12–13 (internal quotation marks omitted). Undoubtedly, federal regulation in this area is 

more pervasive today. But our task remains unchanged:

to determine whether the federal scheme discloses a clear 

and manifest congressional intent to displace state law. 

The Court gives short shrift to our presumption against

pre-emption. Having no express statement of congressional intent to support its analysis, the Court infers from 

stale legislative history and from the comprehensiveness 

of the federal scheme that “Congress made a deliberate

choice not to impose criminal penalties on aliens who seek,

or engage in, unauthorized employment.” Ante, at 13. 
 

Cite as: 567 U. S. ____ (2012) 13 

Opinion of ALITO, J. 

Because §5(C) imposes such penalties, the Court concludes 

that it stands as an obstacle to the method of enforcement 

chosen by Congress. Ante, at 15. 

The one thing that is clear from the federal scheme is 

that Congress chose not to impose federal criminal penalties on aliens who seek or obtain unauthorized work. But 

that does not mean that Congress also chose to pre-empt 

state criminal penalties. The inference is plausible, but 

far from necessary. As we have said before, the “decision 

not to adopt a regulation” is not “the functional equivalent

of a regulation prohibiting all States and their political

subdivisions from adopting such a regulation.” Sprietsma 

v. Mercury Marine, 537 U. S. 51, 65 (2002). With any

statutory scheme, Congress chooses to do some things and 

not others. If that alone were enough to demonstrate preemptive intent, there would be little left over for the 

States to regulate, especially now that federal authority 

reaches so far and wide. States would occupy tiny islands

in a sea of federal power. This explains why state laws

implicating traditional state powers are not pre-empted

unless there is a “clear and manifest” congressional intention to do so. 

Not only is there little evidence that Congress intended

to pre-empt state laws like §5(C), there is some evidence

that Congress intended the opposite result. In making it

unlawful for employers to hire unauthorized aliens, see 8 

U. S. C. §1324a(a), Congress made it clear that “any State 

or local law imposing civil or criminal sanctions (other

than through licensing and similar laws)” upon employers

was pre-empted, §1324a(h)(2). Noticeably absent is any

similar directive pre-empting state or local laws targeting 

aliens who seek or obtain unauthorized employment.

Given that Congress expressly pre-empted certain state 

and local laws pertaining to employers but remained silent 

about laws pertaining to employees, one could infer that 

Congress intended to preserve state and local authority to 
 

 

14 ARIZONA v. UNITED STATES 

Opinion of ALITO, J. 

regulate the employee side of the equation. At the very 

least, it raises serious doubts about whether Congress

intended to pre-empt such authority. 

The Court dismisses any inferences that might be

drawn from the express pre-emption provision. See ante, 

at 14. But even though the existence of that provision 

“does not bar the ordinary working of conflict pre-emption 

principles” or impose a “‘special burden’” against preemption, Geier v. American Honda Motor Co., 529 U. S. 

861, 869–870 (2000), it is still probative of congressional

intent. And it is the intent of Congress that is the “ultimate touchstone.” Retail Clerks v. Schermerhorn, 375 

U. S. 96, 103 (1963).

The Court infers from Congress’ decision not to impose 

federal criminal penalties that Congress intended to preempt state criminal penalties. But given that the express

pre-emption provision covers only state and local laws

regulating employers, one could just as well infer that

Congress did not intend to pre-empt state or local laws 

aimed at alien employees who unlawfully seek or obtain 

work. Surely Congress’ decision not to extend its express 

pre-emption provision to state or local laws like §5(C) is 

more probative of its intent on the subject of pre-emption 

than its decision not to impose federal criminal penalties

for unauthorized work. In any event, the point I wish 

to emphasize is that inferences can be drawn either way.

There are no necessary inferences that point decisively for 

or against pre-emption. Therefore, if we take seriously 

that state employment regulation is a traditional state

concern and can be pre-empted only on a showing of 

“clear and manifest” congressional intent as required by De 

Canas, then §5(C) must survive. “Our precedents establish that a high threshold must be met if a state law is to

be pre-empted for conflicting with the purposes of a federal Act.” Chamber of Commerce of United States of America 

v. Whiting, 563 U. S. ___, ___ (2011) (plurality opinion) 
Cite as: 567 U. S. ____ (2012) 15 

Opinion of ALITO, J. 

(slip op., at 22) (internal quotation marks omitted). I do 

not believe the United States has surmounted that barrier 

here. 

Section 6 

I also disagree with the Court’s decision that §6 is preempted. This provision adds little to the authority that

Arizona officers already possess, and whatever additional 

authority it confers is consistent with federal law. Section 

6 amended an Arizona statute that authorizes warrantless 

arrests. See Ariz. Rev. Stat. §13–3883 (West 2010). Before §6 was added, that statute already permitted arrests

without a warrant for felonies, misdemeanors committed 

in the arresting officer’s presence, petty offenses, and

certain traffic-related criminal violations. See §§13–

3883(A)(1)–(4). Largely duplicating the authority already 

conferred by these prior subsections, §6 added a new 

subsection, §13–3883(A)(5) (West Supp. 2011), that authorizes officers to make warrantless arrests on probable 

cause that the arrestee has committed a “public offense” 

for which the arrestee is removable from the United 

States. A “public offense” is defined as conduct that is

punishable by imprisonment or a fine according to the law

of the State where the conduct occurred and that would be 

punishable under Arizona law had the conduct occurred in

Arizona. See §13–105(27). 

In what way, if any, does §6 enlarge the arrest authority 

of Arizona officers? It has been suggested that §6 confers

new authority in the following three circumstances: (1) 

where the arrestee committed but has not been charged

with committing an offense in another State; (2) where the 

officer has probable cause to believe the arrestee committed an offense for which he was previously arrested but 

not prosecuted; and (3) where the arrestee committed but

has already served the sentence for a removable offense. 

641 F. 3d 359, 361 (CA9 2011). These are exceedingly 
 

 

16 ARIZONA v. UNITED STATES 

Opinion of ALITO, J. 

narrow categories, involving circumstances that will rarely

arise. But such cases are possible, and therefore we must 

decide whether there are circumstances under which federal law precludes a state officer from making an arrest 

based on probable cause that the arrestee committed a

removable offense. 

A 

The idea that state and local officers may carry out

arrests in the service of federal law is not unprecedented.

As previously noted, our cases establish that state and 

local officers may make warrantless arrests for violations 

of federal law and that “in the absence of an applicable 

federal statute the law of the state where an arrest without warrant takes place determines its validity.” Di Re, 

332 U. S., at 589; see also Miller, 357 U. S., at 305 (stating 

that, where a state officer makes an arrest based on federal law, “the lawfulness of the arrest without warrant 

is to be determined by reference to state law”). Therefore, 

given the premise, which I understand both the United

States and the Court to accept, that state and local officers

do have inherent authority to make arrests in aid of federal law, we must ask whether Congress has done anything

to curtail or pre-empt that authority in this particular 

case. 

Neither the United States nor the Court goes so far as to 

say that state and local officers have no power to arrest

criminal aliens based on their removability. To do so 

would fly in the face of 8 U. S. C. §1357(g)(10). Under 

§§1357(g)(1)–(9), the Federal Government may enter into 

formal agreements with States and municipalities under

which their officers may perform certain duties of a federal immigration officer. But §1357(g)(10)(B) makes clear 

that States and municipalities need not enter into those 

agreements “otherwise to cooperate . . . in the identification, apprehension, detention, or removal of aliens not 
 

Cite as: 567 U. S. ____ (2012) 17 

Opinion of ALITO, J. 

lawfully present in the United States.” It goes without 

saying that state and local officers could not provide 

meaningful cooperation in the apprehension, detention,

and ultimate removal of criminal aliens without some 

power to make arrests.

Although §1357(g)(10) contemplates state and local

authority to apprehend criminal aliens for the purpose of 

removal, the Court rejects out of hand any possibility that

officers could exercise that authority without federal 

direction. Despite acknowledging that there is “ambiguity 

as to what constitutes cooperation,” the Court says that

“no coherent understanding of the term would incorporate 

the unilateral decision of state officers to arrest an alien 

for being removable absent any request, approval, or other 

instruction from the Federal Government.” Ante, at 18. 

The Court adopts an unnecessarily stunted view of cooperation. No one would say that a state or local officer

has failed to cooperate by making an on-the-spot arrest to

enforce federal law. Unsolicited aid is not necessarily 

uncooperative.

To be sure, were an officer to persist in making an arrest that the officer knows is unwanted, such conduct 

would not count as cooperation. But nothing in the relevant federal statutes suggests that Congress does not 

want aliens who have committed removable offenses to be 

arrested.2 To the contrary, §1226(c)(1) commands that the

Executive “shall take into custody any alien” who is deportable for having committed a specified offense. And 

§1226(c)(2) substantially limits the circumstances under 

which the Executive has discretion to release aliens held 

in custody under paragraph (1). So if an officer arrests an 

alien who is removable for having committed one of the 

crimes listed in §1226(c)(1), the Federal Government is 

—————— 

2That goes for the Executive Branch as well, which has made the 

apprehension and removal of criminal aliens a priority. See App. 108. 
 

 

18 ARIZONA v. UNITED STATES 

Opinion of ALITO, J. 

obligated to take the alien into custody.

That Congress generally requires the Executive to take

custody of criminal aliens casts considerable doubt on the 

Court’s concern that §6 is an obstacle to the Federal Government’s exercise of discretion. The Court claims that 

the authority conferred by §6 “could be exercised without

any input from the Federal Government about whether

an arrest is warranted in a particular case” and that this

“would allow the State to achieve its own immigration

policy,” resulting in the “unnecessary harassment of some 

aliens . . . whom federal officials determine should not be 

removed.” Ante, at 17. But §1226(c)(1) belies the Court’s 

fear. In many, if not most, cases involving aliens who are 

removable for having committed criminal offenses, Congress has left the Executive no discretion but to take the 

alien into custody. State and local officers do not frustrate the removal process by arresting criminal aliens.

The Executive retains complete discretion over whether 

those aliens are ultimately removed. And once the Federal Government makes a determination that a particular

criminal alien will not be removed, then Arizona officers 

are presumably no longer authorized under §6 to arrest 

the alien. 

To be sure, not all offenses for which officers have authority to arrest under §6 are covered by §1226(c)(1). As 

for aliens who have committed those offenses, Congress 

has given the Executive discretion under §1226(a) over 

whether to arrest and detain them pending a decision on

removal. But the mere fact that the Executive has enforcement discretion cannot mean that the exercise of 

state police powers in support of federal law is automatically pre-empted. If that were true, then state and local 

officers could never make arrests to enforce any federal 

statute because the Executive always has at least some 

general discretion over the enforcement of federal law as a 

practical matter. But even assuming that the express 
 

Cite as: 567 U. S. ____ (2012) 19 

Opinion of ALITO, J. 

statutory grant of discretion in §1226(a) somehow indicates a congressional desire to pre-empt unilateral state 

and local authority to arrest criminal aliens covered by

that provision, §6 is not pre-empted on its face given its 

substantial overlap with §1226(c)(1).

It bears emphasizing that §6 does not mandate the

warrantless apprehension of all aliens who have committed crimes for which they are removable. Instead, it only

grants state and local officers permission to make such 

arrests. The trouble with this premature, facial challenge

is that it affords Arizona no opportunity to implement 

its law in a way that would avoid any potential conflicts

with federal law. For example, Arizona could promulgate 

guidelines or regulations limiting the arrest authority 

conferred by §6 to the crimes specified in §1226(c)(1). And 

to the extent §1226(c)(1) is unclear about which exact

crimes are covered,3 Arizona could go even further and 

identify specific crimes for which there is no doubt an

alien would be removable. The point is that there are

plenty of permissible applications of §6, and the Court 

should not invalidate the statute at this point without at

least some indication that Arizona has implemented it in a

manner at odds with Congress’ clear and manifest intent.

We have said that a facial challenge to a statute is “the

most difficult challenge to mount successfully” because “the

challenger must establish that no set of circumstances

exists under which the [statute] would be valid.” United 

States v. Salerno, 481 U. S. 739, 745 (1987); see also 

Anderson v. Edwards, 514 U. S. 143, 155, n. 6 (1995) 

(applying the Salerno standard in a pre-emption case). As 

to §6, I do not believe the United States has carried that 

—————— 

3 I readily admit that it can be difficult to determine whether a 

particular conviction will necessarily make an alien removable. See 

Padilla v. Kentucky, 559 U. S. ___, ___ (2010) (ALITO, J., concurring in 

judgment) (slip op., at 4). 
 

 

20 ARIZONA v. UNITED STATES 

Opinion of ALITO, J. 

heavy burden. 

B 

Finally, the Court tells us that §6 conflicts with federal

law because it provides state and local officers with “even

greater authority to arrest aliens on the basis of possible 

removability than Congress has given to trained federal 

immigration officers.” Ante, at 16–17. The Court points to

8 U. S. C. §1357(a)(2), which empowers “authorized” officers and employees of ICE to make arrests without a federal warrant if “the alien so arrested is in the United States 

in violation of any [immigration] law or regulation and is

likely to escape before a warrant can be obtained for his

arrest.” Because §6 would allow Arizona officers to make 

arrests “regardless of whether a federal warrant has 

issued or the alien is likely to escape,” ante, at 17, the 

Court concludes that §6 is an obstacle to the accomplishment of Congress’ objectives. But §6 is an obstacle only to

the extent it conflicts with Congress’ clear and manifest

intent to preclude state and local officers from making

arrests except where a federal warrant has issued or the 

arrestee is likely to escape. By granting warrantless 

arrest authority to federal officers, Congress has not manifested an unmistakable intent to strip state and local 

officers of their warrantless arrest authority under state 

law. 

Likewise, limitations on federal arrest authority do not 

mean that the arrest authority of state and local officers 

must be similarly limited. Our opinion in Miller, 357 U. S. 

301, is instructive. In that case, a District of Columbia 

officer, accompanied by a federal officer, made an arrest

based on a suspected federal narcotics offense. Id., at 

303–304. The federal officer did not have statutory authorization to arrest without a warrant, but the local 

officer did. Id., at 305. We held that District of Columbia 

law dictated the lawfulness of the arrest. Id., at 305–306. 
Cite as: 567 U. S. ____ (2012) 21 

Opinion of ALITO, J. 

Where a state or local officer makes a warrantless arrest 

to enforce federal law, we said that “the lawfulness of the 

arrest without warrant is to be determined by reference to 

state law.” Id., at 305. Under §6, an Arizona officer may 

be authorized to make an arrest that a federal officer may 

not be authorized to make under §1357(a)(2). As Miller 

makes clear, that fact alone does not render arrests by

state or local officers pursuant to §6 unlawful. Nor does it 

manifest a clear congressional intent to displace the exercise of state police powers that are brought to bear in aid 

of federal law.