FOR PUBLICATION

UNITED STATES COURT OF APPEALS

 FOR THE NINTH CIRCUIT

FANG LIN AI and DOES 1-1000,

 Plaintiffs - Appellants,

CONCORDE GARMENT

MANUFACTURING CORPORATION,

 Plaintiff-counter-defendant -

Appellant,

 v.

UNITED STATES OF AMERICA,

 Defendant-counter-claimant -

Appellee.

No. 13-17491

D.C. No. 1:11-cv-00014

OPINION

Appeal from the United States District Court

for the District of the Northern Mariana Islands

Ramona V. Manglona, Chief District Judge, Presiding

Argued and Submitted June 10, 2015

Honolulu, Hawaii

Before: WARDLAW, BERZON, and OWENS, Circuit Judges.

Opinion by Judge WARDLAW, Circuit Judge:

Concorde Garment Manufacturing Corporation, and more than 4,000

temporary, nonresident former employees of Concorde, appeal from the district

FILED

DEC 17 2015

MOLLY C. DWYER, CLERK

U.S. COURT OF APPEALS
court’s entry of judgment on the pleadings in favor of the United States.1

 The

district court held that temporary foreign workers in the Commonwealth of the

Northern Mariana Islands (“CNMI”) and their employers are required to pay

Federal Insurance Contributions Act (“FICA”) taxes, which fund Social Security

and Medicare. Section 606(b) of the Covenant governing U.S.-CNMI relations

provides that U.S. laws that impose excise taxes to support the Social Security

system apply to the CNMI as they apply to Guam.

2

 Because FICA is a law that

imposes an excise tax to support the Social Security system, it applies to the CNMI

as it applies to Guam. In turn, FICA applies to all workers and their employers in

Guam, regardless of their citizenship. Therefore, FICA also applies to all workers

and their employers in the CNMI, including Appellants, regardless of their

citizenship. We therefore affirm the district court. 

1

 The district court also entered summary judgment in favor of the United

States on Appellants’ claim for illegal levy. Appellants do not appeal this decision.

2

 The Covenant to Establish a Commonwealth of the Northern Mariana

Islands in Political Union with the United States of America (“Covenant”) was

entered into U.S. law pursuant to Pub. L. No. 94-241, 90 Stat. 263 (1976), and is

codified as a note following 48 U.S.C. § 1801. Several of our opinions have

detailed the history of the Covenant and U.S.-CNMI relations. See, e.g., N.

Mariana Islands v. United States, 399 F.3d 1057, 1058–60 (9th Cir. 2005); Saipan

Stevedore Co. v. Dir., Office of Workers’ Comp. Programs, 133 F.3d 717, 720–21

(9th Cir. 1998).

2
I. Background

Appellants Concorde Garment Manufacturing Corporation (“Concorde”)

and the Chinese national, nonresident workers formerly employed at Concorde’s

facilities in the CNMI (“Employees”) paid FICA taxes from the years 2004 to

2007. In 2008, Appellants filed refund claims for those payments. The Internal

Revenue Service (“IRS”) refunded Concorde’s 2006 FICA taxes but otherwise

took no action on Appellants’ claims. Thereafter, Appellants sued the United

States in the U.S. District Court for the Northern Mariana Islands to recover the

remainder of the FICA taxes they had paid. The United States counter-claimed to

recover the refund of Concorde’s 2006 FICA taxes, which it argued was

erroneously issued. The district court ruled that all workers and their employers in

the CNMI are subject to FICA, regardless of the citizenship of either. 

Appellants timely filed this appeal, arguing that (1) the Covenant was

intended to subject only CNMI citizens, not temporary nonresident foreign

workers, to FICA taxes; (2) even if FICA generally applies to all workers and their

employers in the CNMI, Employees are entitled to the FICA tax exemption for

temporary nonresident Filipino workers in Guam; (3) even if the first two

arguments are rejected, the employee portion of FICA does not apply because it is

an income tax, and only excise and self-employment taxes that support Social

3
Security apply to the CNMI; and (4) the statutory basis for applying FICA to

Appellants is unconstitutionally vague.

3

II. Standard of Review

We review de novo an order granting judgment on the pleadings, accepting

facts alleged by the nonmoving party as true and drawing all inferences in its favor. 

LeGras v. AETNA Life Ins. Co., 786 F.3d 1233, 1236 (9th Cir. 2015). We also

review de novo underlying issues of statutory interpretation and constitutionality. 

Fournier v. Sebelius, 718 F.3d 1110, 1117–18 (9th Cir. 2013), cert. denied, 134 S.

Ct. 1501 (2014).

We have held that “taxing statute[s] must be construed most strongly in

favor of the taxpayer and against the government.” Greyhound Corp. v. United

States, 495 F.2d 863, 869 (9th Cir. 1974). However, “[w]e are not impressed by

the argument that [any doubtful question] should be resolved in favor of the

taxpayer.” White v. United States, 305 U.S. 281, 292 (1938). Thus, “where the

rights of suitors turn on the construction of a [tax] statute . . . it is our duty to

decide what that construction fairly should be,” and “doubts which may arise upon

3

 Appellants adopted the arguments made in American Pacific Textile, Inc. v.

United States, No. 13-16348. We therefore address those arguments here and

resolve issues specific to the American Pacific appeal in a concurrently filed

memorandum disposition. 

4
a cursory examination of [tax statutes may] disappear when they are read, as they

must be, with every other material part of the statute, and in the light of their

legislative history.” Id. (citation omitted); see also Irwin v. Gavit, 268 U.S. 161,

168 (1925) (“It is said that the tax laws should be construed favorably for the

taxpayers. But that is not a reason for creating a doubt or for exaggerating one

when it is no greater than we can bring ourselves to feel in this case.”). 

Therefore, while tax statutes “are not to be extended by implication beyond

the clear import of the language used,” United States v. Merriam, 263 U.S. 179,

187–88 (1923), we do not mechanically resolve doubts in favor of the taxpayer but

instead resort to the ordinary tools of statutory interpretation. Ultimately, “the

literal meaning of the words employed is most important.”4Id.; see also United

States v. Fei Ye, 436 F.3d 1117, 1120 (9th Cir. 2006) (“If the plain language of a

statute renders its meaning reasonably clear, [we] will not investigate further unless

4

 Appellants view the Covenant as a statute. At the same time, Appellants

adopt arguments made by the American Pacific appellants that depend, somewhat

contradictorily, on interpreting the Covenant not as a statute but instead as a treatylike agreement. Appellants therefore urge us to look more liberally to the

Covenant’s drafting history than we might in construing a statute. See Minnesota

v. Mille Lacs Band of Chippewa Indians, 526 U.S. 172, 202 (1999) (“[R]eview of

the history and the negotiations of the agreements is central to the interpretation of

treaties.”). We believe that the Covenant is best viewed as “a congressionally

approved compact [that] is both a contract and a statute . . . . [such that] resort to

extrinsic evidence of the [Covenant’s] negotiations . . . is entirely appropriate.”

Oklahoma v. New Mexico, 501 U.S. 221, 235 n.5 (1991). 

5
its application leads to unreasonable or impracticable results.”) (internal quotation

marks and citation omitted); N. Mariana Islands v. United States, 279 F.3d 1070,

1074 n.5 (9th Cir. 2002) (“We would be undermining congressional intent if we

were to decline to give effect to what section 502(a)(2) of the Covenant by its

terms requires . . . .”).

We note that the Federal Circuit has ruled in favor of the government and

against the taxpayers in a materially indistinguishable case, a decision which is

persuasive, though not dispositive. See Zhang v. United States, 640 F.3d 1358

(Fed. Cir. 2011) (Zhang II), cert. denied, 132 S. Ct. 2375 (2012).5

 We have

recognized, however, that “‘[u]niformity among Circuits is especially important in

tax cases to ensure equal and certain administration of the tax system.’” Hill v.

Comm’r, 204 F.3d 1214, 1217 (9th Cir. 2000) (quoting Pac. First Fed. Sav. Bank

v. Comm’r, 961 F.2d 800, 803 (9th Cir. 1992)). That is particularly true where, as

here, a circuit split would create two mutually exclusive rules applicable to the

CNMI, leading to uncertainty and obvious forum shopping opportunities. 

5

 In Zhang II, the Federal Circuit reviewed and ultimately affirmed a

thorough opinion by the Court of Federal Claims addressing the same issue. See

Zhang v. United States, 89 Fed. Cl. 263 (2009) (Zhang I). 

6
III. Discussion

A. The CNMI Is “Within the United States” for Purposes of FICA.

1. Covenant § 606(b)

FICA imposes an employer and an employee tax on wages “with respect to

employment.” See 26 U.S.C. §§ 3101(a) (“employee tax”), 3111(a) (“employer

tax”). FICA applies to wages related to work performed “within the United

States,” “irrespective of the citizenship or residence of either” the employee or

employer, id. § 3121(b), and to wages related to work performed “outside the

United States” by a U.S. citizen or resident “as an employee for an American

employer,” id. Section 3121(e)(2) defines the term “United States” when it is used

in a geographical sense to include the Commonwealth of Puerto Rico, the Virgin

Islands, Guam, and American Samoa.

6

 Thus, wages for services performed in

Guam are subject to both the employee and employer provisions of FICA,

“irrespective of the citizenship or residence of either” the employee or the

employer. Id. § 3121(b). 

Section 606(b) of the Covenant, in turn, provides:

6

 “United States” is used in a geographical sense in 26 U.S.C. § 3121(b). 

This is evident from the section’s juxtaposition of “within the United States,” id.

(emphasis added), and “outside the United States,” id. (emphasis added). 

Accordingly, it is undisputed that Guam is “within the United States” for purposes

of FICA. See Zhang II, 640 F.3d at 1367.

7
Those laws of the United States which impose excise and selfemployment taxes to support or which provide benefits from the United

States Social Security System will upon termination of the Trusteeship

Agreement or such earlier date as may be agreed to by the Government

of the Northern Mariana Islands and the Government of the United

States become applicable to the Northern Mariana Islands as they apply

to Guam.

Just as in Guam, then, wages for services performed in the CNMI are subject to

FICA taxes, irrespective of citizenship or residence. See id.; 26 U.S.C. § 3121(b). 

We hold that the district court correctly held that Appellants, who paid and

received wages for services performed in the CNMI, are required to pay FICA

taxes on those wages, even though Employees were temporary nonresident

Chinese nationals.7

2. Covenant § 606(b) is not limited to citizens or residents of Guam or the

CNMI.

Appellants attempt to steer us away from this straightforward conclusion,

which flows directly from the plain language of Covenant § 606(b), by advocating

a citizenship-based application of FICA to the CNMI. They argue that the phrase

in Covenant § 606(b) “as they apply to Guam” is ambiguous, and that the term

“Guam” does not mean “Guam,” but actually means “the people who reside in or

7

 We discuss whether the FICA tax on employee wages is “a law[] of the

United States which impose[s] excise and self-employment taxes to support . . . the

United States Social Security System” in Section III.C.

8
who are citizens of [that] geographic area[].”8

 From this manufactured ambiguity,

Appellants assert that § 606(b)’s reference to the CNMI is also ambiguous and

could refer to persons in the CNMI, rather than to the geographic area itself. 

Appellants then argue that § 606(b) does not refer to all the people in the CNMI,

but instead refers only to citizens of the CNMI. Under this tortured reading of the

Covenant, Appellants conclude that § 606(b) subjects only CNMI citizens and their

employers to FICA taxes. 

 There is no plausible method by which to arrive at Appellants’ conclusion

from the plain language of the Covenant and, were § 606(b) amenable to a

citizenship-based application, we would decline to adopt that construction because

FICA is incompatible with such an application.

To begin with, § 606(b) does not mention citizenship or people, and we see

no reason to read those words into the Covenant. Moreover, even if we were to

read references to geographic areas as references to people in those geographic

areas, our reading would not be limited to citizens. The very extrinsic drafting

material Appellants rely upon actually suggests the contrary conclusion. It

8

 See Hearing Before the Subcomm. on Territorial and Insular Affairs of the

H. Comm. on Interior and Insular Affairs on H.J. Res. 549, 550, and 547 to

Approve the “Covenant to Establish a Commonwealth of the Northern Mariana

Islands in Political Union with the United States of America,” 94th Cong. 376

(1975). 

9
suggests that references to Guam or to the CNMI could refer either to the

geographic areas or “to the people who reside in or who are citizens of” those

geographic areas. See 94th Cong. 376. (emphasis added). Thus, there is no

plausible way to limit the applicability of § 606(b)’s cross-reference exclusively to

the citizens as opposed to the residents of the CNMI.9

Further, to the extent that any ambiguity exists as to whether the crossreference to Guam refers to people as opposed to geography, the plain language of

FICA compels us to adopt the geographic application. By its terms, FICA never

applies solely based upon a worker’s citizenship. Rather, FICA applies in two

instances: (1) when work is performed within the United States, and (2) when work

is performed by a U.S. citizen for an American employer. See 26 U.S.C.

§ 3121(b). Therefore, unless we construe § 606(b) to include the CNMI within the

United States geographically, FICA would not require CNMI citizens to pay FICA

taxes unless they were working for an American employer. See id. There is no

indication that FICA was intended to have such a limited effect within the CNMI. 

Indeed, because CNMI citizens became U.S. citizens under the

9

 And FICA, in turn, applies to the CNMI as it applies to Guam—where

nonresident workers are subject to the FICA tax on employee wages because they

performed work “within the United States,” 26 U.S.C. § 3121(b), regardless of

whether they were temporary nonresident workers. 

10
Covenant—meaning they already must pay FICA taxes when working for an

American employer—such an outcome would render § 606(b) meaningless. See

Covenant § 303; 26 U.S.C. § 3121(b).10 We avoid this result and afford § 606(b)

meaning by concluding that, through operation of the cross-reference to Guam, the

CNMI is brought within the geographical territory of the United States for

purposes of FICA.

3. Intervening legislation does not preclude § 606(b)’s applicability. 

Appellants assert that even if they were subject to FICA pursuant to

Covenant § 606(b) as originally drafted, two statutes enacted after the Covenant

was approved, but before § 606(b) became effective in 1986, preclude application

of FICA to Appellants. We disagree. 

First, Appellants look to a 1981 amendment to 42 U.S.C. § 1301, which

altered the definition of the term “State” in the Social Security Act. In doing so,

the amendment extended the application of certain benefit provisions to the CNMI. 

Critically, from Appellants’ perspective, although the amendment expressly

10

 There is a third possibility—that § 606(b) somehow expanded the

definition of “American employer.” Appellants actually raise this argument,

claiming that “CNMI employers—like those of Guam—would be considered

‘American employers’” for purposes of applying 26 U.S.C. § 3121(b). The notion

that § 606(b)—which applies FICA to the CNMI as it applies to Guam—is

somehow intended narrowly to expand the definition of American employer is

nonsensical, and we need not elaborate on this conclusion. 

11
mentioned both the CNMI and Guam, a different menu of benefits was extended to

each. See 42 U.S.C. § 1301(a)(1) (1982). Appellants assert that this amendment

demonstrates Congress’s intent to treat Guam and the CNMI differently, and that it

is therefore improper to mechanically substitute the CNMI for Guam in Covenant

§ 606(b). 

This argument is without merit, and like the Federal Circuit, we reject it. 

See Zhang II, 640 F.3d at 1368 (“Contrary to Appellants’ arguments, Congress did

not subsequently abandon the substitution of Guam for the CNMI by enacting 42

U.S.C. § 1301.”); see also Zhang I, 89 Fed. Cl. at 281–82. Before the amendment

to § 1301, Social Security benefits in the CNMI were linked to benefits in Guam

pursuant to Covenant § 606(b). The amendment operated to eliminate the benefit

parity between the two territories. But there is no indication that Congress

intended its amendment to Social Security benefits to extend to FICA taxes. 

Indeed, far from supporting Appellants’ conclusion, that Congress did not amend

any taxation provisions when it amended the benefits provisions confirms

Congress’s intent that FICA taxes remain applicable to the CNMI as to Guam. 

Thus, the CNMI’s FICA tax treatment remains linked to Guam’s pursuant to

Covenant § 606(b). 

12
Second, Appellants direct us to Section 19 of the Act of 1983, Pub. L. No.

98-213, 97 Stat. 1459. U.S.-CNMI relations were governed by a Trusteeship

Agreement following World War II. During the unexpectedly delayed transition

from the Trusteeship Agreement to the Covenant, CNMI citizens did not meet the

U.S. citizenship requirement included in many statutory benefit provisions.11 As

the Federal Circuit has explained, § 19’s purpose was “to accelerate CNMI

citizens’ receipt of certain statutory benefits to which they otherwise would not

have been entitled until termination of the Trusteeship Agreement.” Zhang II, 640

F.3d at 1368. The Act accomplished this purpose by waiving the U.S. citizenship

requirement for certain benefits. Section 19 of the Act provides: 

(a) The President may . . . provide that the requirement of United States

citizenship or nationality provided for in any of the statutes listed on

pages 63–74 of the Interim Report . . . shall not be applicable to the

citizens of the Northern Mariana Islands. . . . 

11

 Covenant § 504 created a Commission on Federal Laws. The Commission

was tasked with making recommendations to Congress about the application of

certain U.S. laws to the CNMI during the interim period before termination of the

Trusteeship Agreement. In the Commission’s First Interim Report, it observed that

“[m]any federal laws require United States citizenship as a prerequisite to

enjoyment of rights and privileges conferred by those laws.” Interim Report of the

N. Mariana Islands Comm’n on Fed. Laws to the Congress of the United States,

4–6 (1982) (“Interim Report”). The Commission concluded that CNMI citizens

should enjoy these rights and privileges during the possibly prolonged period

before the termination of the Trusteeship Agreement, and it therefore proposed

legislation that would treat CNMI citizens as United States citizens for purposes of

certain federal statutes already applicable to the CNMI. Id. at 6.

13
(b) A statute which denies a benefit or imposes a burden or a disability

on an alien, his dependents, or his survivors shall, for the purposes of

this Act, be considered to impose a requirement of United States

citizenship or nationality.

Reading the two subsections together, § 19(b) clarifies which of the statutes listed

in the Interim Report referenced in § 19(a) contains a “requirement of United

States citizenship.” Thus, § 19(b) defines the type of statutory provision for which

the President may waive a requirement of United States citizenship pursuant to the

authority granted in § 19(a).

Appellants read § 19(b) out of context when they contend that it actually

reads a U.S. citizenship requirement into all U.S. statutes that “den[y] a benefit or

impose[] a burden or a disability on an alien.” It turns the Act of 1983 on its head

to conclude that § 19(b) excludes aliens from both the benefits and the burdens of a

wide range of laws. The very purpose of the 1983 Act was to include CNMI

citizens, who remained “aliens” until the official termination of the Trusteeship

Agreement in 1986, within benefits programs that explicitly required U.S.

citizenship. We therefore join the Federal Circuit in holding that § 19 of the Act of

1983 has no effect on the applicability of FICA to nonresident workers in the

CNMI. See Zhang II, 640 F.3d at 1368–70. 

14
B. The FICA Exemption for Nonresident Filipino Workers in Guam Does Not

Extend to Nonresident Chinese Workers in the CNMI.

Appellants next argue that even if FICA applies to nonresident workers and

their employers in the CNMI generally, Appellants fit within an exemption to

FICA taxation that Congress created for certain nonresident workers in Guam. The

exemption on which Appellants rely, however, is expressly limited to Filipino

citizens admitted to Guam under H-2 visas. See 26 U.S.C. § 3121(b)(18).12

Pursuant to Covenant § 606(b), then, Filipinos admitted to the CNMI under H-2

visas arguably would be exempt from FICA. However, even if we overlooked the

fact that Employees were not admitted to the CNMI pursuant to H-2 visas, the

exemption remains plainly inapplicable because Employees are Chinese

nationals.13

12

 This section of FICA exempts from the definition of employment any

“service performed in Guam by a resident of the Republic of the Philippines while

in Guam on a temporary basis as a nonimmigrant alien admitted to Guam pursuant

to section 101(a)(15)(H)(ii) of the Immigration and Nationality Act.” 26 U.S.C.

§ 3121(b)(18).

13

 We need not decide whether the exemption would apply to Filipinos in the

CNMI who were not admitted pursuant to H-2 visas but were instead admitted

pursuant to the CNMI’s local immigration law. This is a close question. During

the relevant time period—2004 to 2007—the CNMI was not subject to the

Immigration and Naturalization Act, and instead maintained the authority to create

its own immigration laws. Accordingly, from 2004 to 2007, temporary workers

entered the CNMI pursuant to the CNMI’s Nonresident Workers Act. See 3 N.

(continued...)

15
Moreover, as Appellants concede, Filipinos were not the only temporary

nonresident workers in Guam when the exemption was created. See U.S. House of

Rep., Comm. on the Judiciary, Subcomm. on Immigration, Citizenship, and Int’l

Law, The Use of Temporary Alien Labor on Guam 3–4 (1975). In light of this

demographic reality, Congress’s decision to expressly limit the exemption to

Filipinos, in part because of our nation’s unique political ties with the Philippines,

suggests that the exemption was not meant to cover all nonresident workers in

Guam. In sum, Congress singled out Filipinos for preferential treatment. Because

it is undisputed that Employees are not Filipinos, the exemption does not apply to

them. 

C. FICA and SECA Apply in Their Entirety to the CNMI as They Apply to Guam.

Section 606(b) states that “[t]hose laws of the United States which impose

excise and self-employment taxes to support . . . the United States Social Security

system will . . . become applicable to the [CNMI] as they apply to Guam.”

Covenant § 606(b). Appellants contend that even if FICA generally applies to the

CNMI, the employee portion does not apply because it is an income tax, not an

13

(...continued)

Mar. I. Code § 4411, et seq. Thus, although temporary nonresident Filipinos in the

CNMI are the exact type of worker Congress sought to exempt from FICA, these

workers do not technically satisfy all statutory elements of the exemption.

16
excise or self-employment tax. See 26 U.S.C. § 3101(a) (imposing “on the income

of every individual a tax”). In other words, Appellants read § 606(b) as if it

contains an additional limitation: “Those laws of the United States which impose

only excise taxes and only self-employment taxes to support . . . the United States

Social Security system will . . . become applicable to the [CNMI] as they apply to

Guam.” Appellants misread the provision.

Section 606(b) does not contain the limitation suggested by Appellants, nor

does it state that excise taxes apply in the CNMI as in Guam. Instead, § 606(b)

provides that those laws which impose such taxes apply in the CNMI as in Guam. 

The difference is subtle but crucial: Laws imposing excise taxes, and not simply

the excise taxes themselves, apply in the CNMI as in Guam. In short, if a law

imposes an excise tax to support Social Security, the law—not just that part of the

law imposing an excise tax—applies in the CNMI as in Guam.

14

 Because FICA

imposes an excise tax, it applies in the CNMI as in Guam. And because FICA

14

 Although it might be possible to treat 26 U.S.C. § 3111, the employer

portion of FICA, as a separate law from § 3101, the employee portion, such

treatment is untenable. Both § 3101 and § 3111 rely on § 3121, among other

provisions. Thus, § 3111 is incomplete without the remainder of FICA. Because

§ 3111 cannot be viewed as a “law” in isolation from the overarching statute, the

law at issue in Covenant § 606(b) is not merely the employer portion of FICA. 

The law is instead FICA as a whole, which necessarily includes the employee

portion.

17
subjects employees in Guam to taxation, it subjects employees in the CNMI to

FICA taxes as well.

This plain reading of § 606(b) is reinforced by the section’s additional

reference to laws imposing self-employment taxes. While the reference to laws

imposing excise taxes is sufficient to capture FICA in its entirety, self-employment

taxes that support Social Security are not included in FICA. Instead, they are

found in the Self-Employment Contributions Act (“SECA”). See 26 U.S.C. 

§§ 1401–03. Therefore, while there are three general taxes that support the Social

Security system—the employee FICA tax, the employer FICA tax, and SECA

taxes—there are only two laws imposing those taxes—FICA and SECA. And

Covenant § 606(b)’s language is designed to render both laws applicable to the

CNMI as they apply to Guam.

Any doubt that this reading is correct is dispelled when § 606(b) is

considered in the context of the Covenant as a whole. Another of the Covenant’s

provisions, Section 601(a), provides that “[t]he income tax laws in force in the

United States” apply in the CNMI “in the same manner as those laws are in force

in Guam.” Covenant § 601(a) (emphasis added). The reason for the omission of

any specific reference to income taxes in § 606(b) is therefore apparent: Section

601(a) already makes clear that such taxes are applicable in the CNMI. Section

18
601(a) thus clarifies that “[t]hose laws of the United States which impose excise

and self-employment taxes to support . . . the United States Social Security

System” do indeed include the employee portion of FICA. 

To the extent that the phrase “those laws” is ambiguous, in that the laws

could be broken down further to include only 26 U.S.C. § 3111(a) (the portion of

FICA imposing an excise tax), rather than all of FICA, we may look to extrinsic

drafting sources to resolve this ambiguity. See Diamond v. Chakrabarty, 447 U.S.

303, 315 (1980) (“[O]ur obligation is to take statutes as we find them, guided, if

ambiguity appears, by the legislative history and statutory purpose.”). The

available extrinsic evidence overwhelmingly suggests that the drafters intended

that all FICA taxes apply. 

Both the House and Senate Reports produced in connection with Congress’s

approval of the Covenant provide: “Subsection (b) [of Covenant § 606] assures

that the laws of the United States which impose taxes to support . . . the United

States Social Security System will become applicable to the Northern Marianas as

they are applicable to Guam upon termination of the Trusteeship Agreement . . . .”

H.R. Rep. No. 94–364, at 11 (1975); S. Rep. No. 94–433, at 83 (1975). As the

Federal Circuit aptly observed, “[t]he reports do not distinguish the employer

19
FICA tax from the employee FICA tax, nor do they suggest that one tax applies but

the other does not.” Zhang II, 640 F.3d at 1374. 

The Section–by–Section Analysis of the Covenant—published by the

Marianas Political Status Commission, which assisted in the Covenant’s

drafting—also does not distinguish between the employer and employee FICA

taxes. See Zhang II, 640 F.3d at 1375 (noting that “Congress considered the

Section–by–Section Analysis prior to approving the Covenant”) (citing S. Rep. No.

94–433, at 65–94); N. Mariana Islands, 399 F.3d at 1065 (“We have relied in

previous opinions on the Marianas Political Status Commission’s authoritative

Section–by–Section Analysis of the Covenant to assist us in discerning the

meaning of the Covenant.”) (internal quotation marks omitted). Describing

Covenant § 606(b), the Section–by–Section Analysis states:

Subsection (b) [of § 606] assures that the laws of the United States which

impose taxes to support or which provide benefits from the United States

Social Security System will become applicable to the Northern Marianas

as they are applicable to Guam upon termination of the Trusteeship

Agreement. . . . At this time as well, those laws of the United States

which impose taxes to support the United States Social Security System

will become applicable. The reason that the Covenant is structured in a

way which does not make the United States social security laws

applicable immediately is that the taxes which are imposed to support the

social security system are very burdensome as compared to the taxes

which are paid by the people of the Northern Marianas today . . . 

[T]hese laws will become effective in the Northern Marianas no later

20
than termination of the Trusteeship, at which time the entire Covenant

will be effective. 

Marianas Political Status Comm’n, Section–by–Section Analysis of the Covenant to

Establish a Commonwealth of the Northern Mariana Islands, 80–81 (1975)

(emphasis added). 

Likewise, the Commission on Federal Laws, see Covenant § 504, did not

distinguish between the two taxes. In pertinent part, the summary section of the

Commission’s Second Interim Report states: “Employers and employees in the

Northern Mariana Islands are made subject to taxes imposed by [FICA] to support

the federal social security system at the time the social security systems of the

Northern Mariana Islands and the United States are merged . . . .” Second Interim

Report of the N. Mariana Islands Comm’n on Fed. Laws to the Congress of the

United States 415 (1985). More specifically, the Second Interim Report contains a

section entitled “Employment Taxes,” which explains that under FICA, “[t]he

employer and employee are each required to pay taxes.” Id. at 465. 

In light of this legislative history, we resolve any ambiguity in § 606(b) by

concluding that the word “laws” refers to the entire law containing the tax in

question—i.e., FICA and SECA. See also Zhang I, 89 Fed. Cl. at 281 (“The[]

legislative documents are uniform in their treatment of section 606(b),

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unambiguously demonstrating that all FICA tax provisions were intended to apply

to the CNMI.”). 

Moreover, reading § 606(b) to apply the employer portion of FICA without

the employee portion would mean subjecting CNMI employers but not CNMI

employees to FICA taxation, even though many of the exempt CNMI employees

would be able to receive benefits under the system. See Zhang II, 640 F.3d at 1363

(discussing the Court of Federal Claims’ conclusion that Congress clearly intended

to avoid such an absurd result).

Ultimately, the text of § 606(b) provides that FICA—a law imposing an

excise tax—applies to the CNMI as it applies to Guam. In Guam, employees are

subject to FICA, and thus the same is true in the CNMI, regardless of whether that

tax is an excise tax or an income tax. It is the law containing the excise tax that

applies to the CNMI as to Guam, not merely the “excise tax” itself. See Covenant

§ 606(b).15 

15

 We note that the district court also relied on Covenant § 601(a) and (c) in

concluding that FICA applies in its entirety to the CNMI. However, we may

affirm on any ground supported by the record. See Columbia Pictures Indus., Inc.

v. Fung, 710 F.3d 1020, 1030 (9th Cir. 2013), cert. dismissed, 134 S. Ct. 624

(2013). Because we hold that Covenant § 606(b) renders both employee and

employer FICA taxes applicable to the CNMI, we do not reach the parties’

alternative contentions concerning the applicability of Covenant § 601(a) and (c). 

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D. The Applicability of FICA to Appellants Through the Covenant Is Not 

Unconstitutionally Vague.

Appellants argue that, because the IRS has not explained consistently why

FICA taxes apply to them, the statutory scheme is unconstitutionally vague. See

Vill. of Hoffman Estates v. Flipside, Hoffman Estates, Inc., 455 U.S. 489, 497–99

(1982) (explaining that the void for vagueness doctrine applies to civil statutes). 

Contrary to Appellants’ suggestion, however, the question is not whether the

government applied or interpreted FICA consistently. Instead, the question is

whether the scheme that subjects Appellants to FICA taxes is “so vague and

indefinite as really to be no rule or standard at all,” Boutilier v. INS, 387 U.S. 118,

123 (1967), or whether a person of ordinary intelligence could understand that the

scheme requires payment of FICA taxes, see Ass’n des Eleveurs de Canards et

d’Oies du Quebec v. Harris, 729 F.3d 937, 946 (9th Cir. 2013). 

FICA’s applicability to Appellants is not unclear, as evidenced most

prominently by Appellants’ payment of FICA taxes from 2004 through 2007. See,

e.g., United States v. Moore, 109 F.3d 1456, 1467 (9th Cir. 1997) (finding Gun

Control Act was not unconstitutionally vague where “[t]he record show[ed] that

both [defendants] understood their respective legal obligations”). Moreover, the

Court of Federal Claims, the Federal Circuit, and the District Court for the

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Northern Mariana Islands have each reached the same conclusion—that Appellants

are subject to FICA taxes. If anything, that these courts have arrived at this

conclusion by different statutory routes suggests that the relevant statutory scheme

advised Appellants in multiple ways that they must pay FICA taxes. 

Appellants themselves, all courts to consider the issue, and the IRS have

consistently read the statutory scheme as requiring Appellants to pay employer and

employee FICA taxes. Appellants’ position was not frivolous, and they were

justified in requesting a refund from the IRS. But having a colorable argument that

FICA taxes do not apply does not render the statute unconstitutionally vague.

16

IV. Conclusion

For the foregoing reasons, we AFFIRM the district court’s entry of

judgment on the pleadings in favor of the United States on Appellants’ claims, as

16

 Moreover, it does not appear that Appellants face any penalty. They

simply must pay the tax. This is not a situation where a party acted in reliance on

the law (or in ignorance of a law due to lack of clarity) only to be subject to a

penalty or, worse yet, criminal sanctions, because it acted in accordance with a

reasonable understanding of the law. Thus, to the extent that vagueness concerns

apply at all in this case, those concerns are de minimis. See, e.g., Groome

Resources Ltd., L.L.C. v. Par. of Jefferson, 234 F.3d 192 (5th Cir. 2000) (affirming

entry of permanent injunction against Parish, which delayed granting a zoning

accommodation to the developer of an Alzheimer’s care facility, where the delay

would impose financial penalties upon the developer and the Parish argued in part

that statutory vagueness justified the delay). 

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well as the district court’s entry of judgment on the pleadings in favor of the

United States on the United States’ counterclaim. 

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COUNSEL

Craig E. Stewart (argued), Kelsey Israel-Trummel, and Edward Patrick Swan, Jr.,

Jones Day, San Francisco, California; Steven P. Pixley, Saipan, Northern Mariana

Islands, for Plaintiff-Counter-Defendant-Appellant Concorde Garment

Manufacturing. 

Colin M. Thompson, Thompson Law Office, LLC, Saipan, Northern Mariana

Islands, for Plaintiffs-Appellants Fang Lin Ai, et al. 

Bridget M. Rowan (argued), Tamara W. Ashford, Teresa T. Milton, United States

Department of Justice, Tax Division, Washington, District of Columbia; Alicia

A.G. Limtiaco, United States Attorney, United States Attorney’s Office, Saipan,

Northern Mariana Islands, for Defendant-Counter-Claimant-Appellee.

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