The safety of air travel, particularly after the terrorist attacks of September 11, 2001, has been an important priority for the U.S. government. The Aviation and Transportation Security Act of 2001 created the Transportation Security Administration (TSA) and charged it with ensuring the security of all modes of transportation, including civil aviation. The TSA is responsible for prescreening all potential commercial airline travelers before they board an aircraft. Pursuant to this responsibility, TSA uses the "No Fly" list to identify individuals who pose a threat to aviation safety. Persons attempting to board an aircraft who are matched to an identity on the No Fly list are not allowed to board. Although the current number and identity of persons on the No Fly list is not a matter of public record, some recent news reports claim that more than 80,000 people are currently on the list. However, some persons have claimed that their alleged placement on the list was the result of an erroneous determination by the government that they posed a national security threat. In some cases, it has been reported that persons have been prevented from boarding an aircraft because they were mistakenly believed to be on the No Fly list, sometimes on account of having a name similar to another person who was actually on the list. The Department of Homeland Security (DHS) operates a redress process for travelers who wish to contest their right to board an aircraft, but this procedure has been challenged in federal court as violating the Fifth Amendment right to due process. After an adverse ruling in a federal district court case in 2014, the executive branch revised the process. This report provides an overview of the operation of the government's watchlists, examines some of the legal issues implicated by challenges to the No Fly list, and describes recent case law on the matter. The National Counterterrorism Center (NCTC) serves as the central information bank for the U.S. government on "known and suspected terrorists and international terrorist groups." It is the government's principal organization for "analyzing and integrating" intelligence concerning terrorism and counterterrorism. The NCTC maintains the Terrorist Identities Datamart Environment (TIDE), the central repository of the U.S. government containing derogatory information about suspected international terrorists. Based on evaluations of intelligence information, agencies in the intelligence community (IC) nominate individuals known or suspected to be international terrorists and forward the names to the NCTC. Using a non-exclusive list of possible factors, the NCTC determines if each name merits inclusion on the list. As of June 30, 2016, according to the NCTC, about 1.5 million persons were included in TIDE, and about 15,000 were U.S. persons (citizens and lawful permanent residents). TIDE contains all of the government's information regarding persons "known or appropriately suspected to be or to have been involved in activities constituting, in preparation for, in aid of, or related to terrorism (with the exception of purely domestic terrorism information)." Due to the national security importance of this information, the contents of the database are classified. The NCTC "exports" an unclassified subset of the data, including biometric and biographic identifiers, to the Terrorist Screening Center (TSC), which, in turn, operates the Terrorist Screening Database (TSDB). In contrast to TIDE (operated by NCTC), the TSDB (operated by TSC) does not include "derogatory intelligence information." Instead, it consists of "sensitive but unclassified terrorist identity information consisting of biographic identifying information such as name or date of birth or biometric information such as photographs, iris scans, and fingerprints." Established pursuant to Homeland Security Presidential Directive 6, the TSC is managed by the Federal Bureau of Investigation (FBI) and receives support from various federal agencies. The information in the TSDB is obtained from two primary sources. First, as mentioned above, TIDE provides information on the identity of suspected international terrorists. Second, the FBI's Automated Case Support System (ACSS) provides additional information on suspected domestic terrorists directly to the TSC. Whether receiving information from TIDE or ACSS, the TSC will review each file to ensure that it satisfies the government's watchlist standards before adding the name to the TSDB. The information received by TSC must satisfy two requirements to merit inclusion on the TSDB. First, the "biographic information associated with a nomination must contain sufficient identifying data so that a person being screened can be matched or disassociated from a watchlisted terrorist." Second, the "facts and circumstances" must "meet the reasonable suspicion standard of review." This means "articulable facts which, taken together with rational inferences, reasonably warrant the determination that an individual is known or suspected to be or has been engaged in conduct constituting, in preparation for, in aid of, or related to terrorism and terrorist activities." This standard was not mandated by statute, but was "adopted by internal Executive Branch policy and practice." In addition, a 2014 district court opinion stated that there was a "secret exception to the reasonable suspicion standard," but the "nature of the exception and the reasons ... for nomination are claimed to be state secrets." As mentioned above, in contrast to the classified contents of TIDE, the TSDB contains sensitive, but not classified, information about the identity of suspected terrorists. The unclassified nature of the list permits a broad range of federal, state, and local organizations to access the data. Accordingly, the TSC provides various frontline screening agencies with subsets of the TSDB for use in combating terrorism. These watchlists are tailored in accordance with the agency's mission(s) and statutory authorities. For the purposes of monitoring flights, TSA receives two such lists: the No Fly list and the Selectee list. People on the first are prohibited from boarding an American airline or any flight that comes in contact with U.S. territory or airspace. Those on the second are subject to enhanced screening procedures when they attempt to do so. The No Fly and Selectee lists have their own substantive requirements for inclusion, which executive officials have stated are more stringent than the reasonable suspicion standard for placement on the TSDB. In order to qualify for inclusion on the No Fly or Selectee lists, a nomination must "establish[] a reasonable suspicion that the individual meets additional heightened derogatory criteria that goes above and beyond the criteria required for inclusion in the broader TSDB." When a person is placed on the list, they will not receive notice; instead, they will simply be denied boarding or subjected to enhanced screening procedures if they attempt to board a plane. However, in a departure from the traditional requirements for inclusion on the No Fly list, after the failed terrorist attack of the so called "underwear bomber," who attempted to destroy a commercial plane traveling from Amsterdam to Detroit on Christmas Day 2009, the NCTC and TSC were ordered, following an interagency meeting, to add a number of individuals from the TIDE database to the No Fly list. This included a number of "individuals without any information indicating a personal involvement in terrorism." Accordingly, a number of individuals were placed on the No Fly list who may not have met the normal standards for inclusion. Subsequently, TSC, in coordination with the FBI and other intelligence agencies, conducted a review of all the individuals who had been upgraded. This review was completed more than two years after the original upgrading. A 2014 Department of Justice (DOJ) Office of Inspector General audit expressed "concerns about the TSC's ability to ensure that all watchlist records that were modified as a result of the attempted attack were reviewed and returned to the appropriate individualized status." The precise guidelines and particular factors the government relies on to place individuals on terrorist watchlists are not made public. The criteria for placement on the No Fly list, as well as whether a person is on the No Fly list, are considered "Sensitive Security Information" (SSI) and have not been publicly released by the federal government. Initially, TSA required aircraft operators to screen passengers by matching data against the No Fly and Selectee lists. Following the release of the 9/11 Commission Report , the Intelligence Reform and Terrorism Prevention Act of 2004 altered this arrangement by requiring TSA to conduct the matching itself. The act also requires aircraft operators to provide passenger information to TSA for prescreening purposes. TSA issued the Secure Flight Final Rule on October 28, 2008, implementing the act's requirements. Under the program, TSA requires aircraft operators to collect Secure Flight Passenger Data (SFPD) from passengers and provide it to TSA. SFPD includes passengers' full name, date of birth, gender, and can also include certain non-personal information, such as itinerary and a travel record number. The information is collected when a potential passenger makes a flight reservation. This information must be provided to TSA about 72 hours prior to the flight. For reservations that occur after this deadline, aircraft operators must provide the SFPD as soon as possible. TSA then matches the data with the No Fly, Selectee, and Centers for Disease and Control and Prevention (CDC) Do Not Board list. The potential matches are compared to the TSA Cleared List, which contains the identities of individuals who have been cleared through the DHS redress process. TSA then performs manual reviews of potential matches to ensure individuals are included on the No Fly and Selectee lists, which may include the consultation of other databases. Following this process, TSA will prohibit certain passengers from receiving a boarding pass. If such passengers arrive at the airport, air carriers may send updated passenger information to TSA for rematching or may call Secure Flight to resolve an issue. This process may involve contact between Secure Flight and the Terrorist Screening Center to confirm or eliminate a match. At the conclusion of this procedure, a passenger will either be cleared to fly, designated as a selectee for enhanced screening, or barred from boarding the aircraft. Since 2009, Secure Flight has evolved to assign passengers a risk category: high risk, low risk, or unknown. The Secure Flight Final Rule provides that TSA has discretion to check against the entire TSDB and other watchlists when warranted for security reasons, and has developed new lists for passengers considered high risk and subject to enhanced screening. First, working with Customs and Border Protection—which has access to additional information about international travelers—Secure Flight has developed two lists to identify certain individuals for enhanced screening. TSA analysts examine relevant intelligence information to identify factors that may denote a passenger who poses an elevated risk. TSA then develops rules based on these factors, and these rules are provided to CBP, which uses the Automated Targeting System-Passenger to identify individuals who correspond to the rules. Those passengers are then subject to enhanced screening. Second, beginning in April 2011, TSA began matching against an Expanded Selectee List, which includes records in the TSDB with a full name and date of birth that are not on the No Fly or Selectee List but do meet the Terrorist Screening Center's reasonable suspicion standard to qualify as a known or suspected terrorist. Individuals identified in this list are also subject to enhanced screening. A number of travelers who dispute any connection to terrorism have alleged that they have been denied boarding on commercial aircraft. A denial of entry can occur, for example, when a person's name and/or date of birth correspond or are similar to the identity of someone in the government's watchlist database. The Implementing Recommendations of the 9/11 Commission Act of 2007 directed DHS to create an Office of Appeals and Redress for people who believe they have been mistakenly denied boarding or subjected to heightened screening for security reasons. Pursuant to these requirements, DHS established the Traveler Redress Inquiry Program (TRIP) to resolve such issues. In general, the program is designed to offer an efficient remedy for travelers who encounter difficulty with the government's screening process and to centralize a multiagency process of reviewing and responding to any traveler complaints. Following litigation concerning the constitutionality of the redress procedures available to plaintiffs who challenge their inclusion on a government watchlist, the government has revised the DHS TRIP redress procedures. Prior to this revision, passengers who were denied boarding or subjected to additional screening procedures could seek redress by filing a complaint online or by mailing a complaint form. All travelers who did so were assigned a redress number. If DHS decided that a person seeking redress was a match or near match to an identity contained in the TSDB, the agency referred the potential match to the redress unit of the TSC. TSC then determined if the person was an actual match with the identity of someone in the TSDB. If the person was determined to be a match, TSC next determined whether the person should continue to be in the TSDB; and, finally, whether the person should continue to be on the No Fly or Selectee list. Those travelers determined not to match a person in the TSDB were added to the DHS TRIP Cleared List and received a corresponding traveler redress number. Subsequently, a traveler could enter his or her redress number when purchasing an airline ticket. If travelers were on the DHS TRIP Cleared List, they could be cleared by Secure Flight, and presumably would receive authorization to board an aircraft. When the review process was completed, DHS TRIP sent a letter to travelers notifying them that review was complete. The letter, however, did not confirm or deny whether an individual was on the No Fly list or in the TSDB. Notifications usually provided that travelers could seek judicial review in a U.S. court of appeals under 49 U.S.C. § 46110. That review consisted of an ex parte and in camera examination by the court of the administrative record provided by the government containing the evidence it relied upon. If the court disagreed with the government's determination, the court could remand the case to the agency for further consideration. Even after judicial review by a U.S. court of appeals, travelers were never informed of their status on any watchlist or whether they would be permitted to board an aircraft traveling to, from, or within the United States in the future. Instead, a person on a No Fly list who attempted to board a plane would simply be denied boarding. The DHS TRIP redress process did not provide travelers with reasons for inclusion on the list, or a hearing where they might challenge their inclusion on the list. At no point did travelers have the opportunity "to contest or to offer corrections to the record on which any such determination may be based." The "government's policy [was] never to confirm or to deny an individual's placement on the No Fly list." The original redress process was challenged by a number of individuals denied boarding, including on the grounds that it purportedly violated the Due Process Clause of the Constitution. Following an adverse ruling by a federal district court, the government revised the DHS TRIP procedures. Under the current process described by the government, a U.S. person denied boarding who has applied for redress under DHS TRIP will receive a letter indicating whether he or she is on the No Fly list. If so, this letter will also notify the individual that he or she may elect to receive or submit additional information. If a U.S. person requests further information, DHS TRIP will typically provide a second response which "will identify the specific criteria or criterion under which the individual has been placed on the" list, "includ[ing] an unclassified summary of information supporting the individual's No Fly List status." This second letter informs recipients that they may seek further review of their status and to submit information regarding whether their placement on the No Fly list is warranted. Upon receipt of an individual's response, DHS TRIP forwards the case to the TSC Redress office. TSC then reviews the relevant materials and provides a recommendation to the TSA Administrator regarding whether a person should remain on the list. Next, the TSA Administrator will review that recommendation and issue a final decision either removing the individual from the No Fly list, maintaining him or her on the list, or remanding the case to TSC for further information. This final order will be delivered to the individual petitioner as well as TSC. If the order removes the individual from the No Fly List, the TSC Redress Office will update the relevant information to the TSDB and the screening systems that receive information from the TSDB. The Fifth Amendment of the U.S. Constitution provides that no person shall be "deprived of life, liberty, or property, without due process of law." This protection extends to U.S. citizens and noncitizens who have sufficient ties to the United States. Courts have developed two major legal doctrines concerning the protection of rights and liberty interests under the Due Process Clause—procedural and substantive due process. "Procedural due process imposes constraints on governmental decisions which deprive individuals of 'liberty' or 'property' interests within the meaning of the Due Process Clause of the Fifth or Fourteenth Amendment." As explained below, the particular procedures required may vary according to the situation. Substantive due process encapsulates the notion that the Due Process Clause "provides heightened protection against government interference with certain fundamental rights and liberty interests." Courts have found that placement on the No Fly list can potentially implicate procedural and substantive due process rights. However, because claims alleging substantive due process violations are somewhat underdeveloped as of yet, this report primarily examines procedural due process claims, which have received more extensive analysis by federal courts. Some travelers who challenge their placement on the No Fly list and the government's redress process have alleged that their right to international travel has been deprived without due process of law. Courts assessing procedural due process claims first ask "whether the plaintiff has been deprived of a [constitutionally] protected interest." If so, courts next "consider whether the procedures used by the government in effecting the deprivation 'comport with due process.'" Placement on the No Fly list can impede one's ability to travel internationally. While a "right to travel" is not expressly mentioned in the Constitution, the Supreme Court has recognized a right to travel as "a part of the 'liberty' of which the citizen cannot be deprived without due process of law under the Fifth Amendment." The right to interstate travel is less susceptible to government restraint than the right to international travel, as the Court has described the former as "virtually unqualified." The right to international travel is nonetheless a "liberty protected by the Due Process Clause." However, the right to international travel is subject to "reasonable governmental regulations," and not every restriction on a person's right to travel will raise a significant due process concern. In assessing whether a governmental policy infringes upon such a right, courts will often examine the scope of the policy and the degree to which it impairs the ability of a person to feasibly travel. Not every impediment to travel is considered a deprivation of a constitutionally protected interest. In Gilmore v. Gonzales for example, the U.S. Court of Appeals for the Ninth Circuit rejected a constitutional challenge to the TSA's requirement that an airline passenger present identification before boarding an interstate flight. The court noted that the plaintiff was barred from only one form of interstate travel, and ruled that the government's policy did not violate the plaintiff's right to interstate travel "because the Constitution does not guarantee the right to travel by any particular form of transportation." The court explained that the "burden" of presenting identification was not unreasonable and "other forms of travel remain[ed] possible." Several federal courts, however, have distinguished certain challenges to placement on the No Fly list from this case and determined that placement on the No Fly list can deprive someone of a constitutionally protected liberty interest in international travel. For example, one district court noted that Gilmore concerned a plaintiff's right to fly within the United States, while placement on the No Fly list bars international flight. While there may be "alternatives to flying for domestic travel within the continental United States," the court reasoned, flying is often the only feasible method of international travel. Further, Gilmore concerned a requirement to show identification in order to board an airline, while placement on the No Fly list bars flying indefinitely. For these courts, placement on the No Fly list is a deprivation of a constitutionally protected interest, and the government's procedures must therefore comport with due process. Another liberty interest that can be implicated by placement on the No Fly list—thus triggering procedural due process protection—is harm to one's reputation combined with a denial of a legal right or status. Under this "stigma-plus" doctrine, a plaintiff can establish a due process claim by showing (1) "the public disclosure of a stigmatizing statement by the government, the accuracy of which is contested" and (2) "the denial of 'some more tangible interest' ... or the alteration of a right or status recognized by state law." For example, one federal district court found that the plaintiffs, who allegedly had names similar to names on the No Fly list and were regularly subjected to enhanced screening procedures in view of their fellow travelers, satisfied the first prong because public association with terrorism was sufficiently stigmatizing. However, the court found that the plaintiffs failed to satisfy the second prong, because they did not show a "tangible harm." The court noted that the "Plaintiffs do not have a right to travel without any impediments whatsoever," and "have not alleged any tangible harm to their personal or professional lives that is attributable to their association with the No-Fly List, and which would rise to the level of a Constitutional deprivation of a liberty right." In contrast, another federal district court found that plaintiffs who had actually been prevented from flying met both factors. The first was met because placement on a No Fly list "carries with it the stigma of being a suspected terrorist that is publicly disclosed to airline employees and other travelers." The second was met because the plaintiffs suffered a "change in legal status"—they were legally barred from traveling by air to or from the United States, and they would have engaged in such travel had they not been placed on the No Fly list. Nonetheless, another district court, in weighing a challenge to placement on the No Fly list, found the stigma plus doctrine was not satisfied because the plaintiff failed to sufficiently allege facts that would "give rise to an inference that the stigmatizing statements reached the other passengers so as to cause harm to Plaintiff's reputation." As explained above, if a court finds that the government has deprived someone of a constitutionally protected liberty interest—one's right to international travel, for example—then the government must provide that person with due process. This usually requires the government to provide the person with notice of the deprivation and an opportunity to be heard before a neutral party. The Supreme Court has explained, however, that due process is not a "technical conception with a fixed content unrelated to time, place, and circumstances." Instead, the concept is "flexible and calls for such procedural protections as the particular situation demands." Consequently, the precise type of notice, the manner and time of a hearing, and the identity of the decisionmaker can vary according to the situation. When determining the proper procedural protections in a given situation, courts will weigh the private interests affected against the government's interest. In Mathews v. Eldridge , the Supreme Court articulated the balancing test for deciding what procedural protections are required when the government deprives someone of life, liberty, or property. A court must examine three broad factors: First, the private interest that will be affected by the official action; second, the risk of an erroneous deprivation of such interest through the procedures used, and the probable value, if any, of additional or substitute procedural safeguards; and finally, the Government's interest, including the function involved and the fiscal and administrative burdens that the additional or substitute procedural requirement would entail. Therefore, as explained more fully below, when a court confronts a challenge to a governmental deprivation of a constitutionally protected liberty interest, a court will balance each of these factors in order to determine what procedural protections due process requires. As explained above, the right to international travel is a constitutionally protected liberty interest that some courts have found to be infringed by placement on the No Fly list. In assessing a procedural due process challenge to the governmental procedures when a person's liberty is infringed, courts will first weigh the private interest affected by the government's action. In assessing the significance of the deprivation, the Supreme Court has examined a number of different factors, including the severity, length, and the finality of a deprivation. For example, the Court has found the termination of welfare benefits—which are based on financial need—to be more severe than the termination of disability benefits, which are not. In the latter case, the Court has ruled, less procedural protections are required. Similarly, the Court has noted the difference between absolute termination and a temporary suspension from one's employment. Again, the latter requires less procedural protections. The weight given the private interest by courts weighing challenges to placement on the No Fly list might turn on the level of generality the court uses to interpret the deprivation. One might argue, for example, that for most people, air travel is often the only feasible method for international travel available. Arguably, placement on the No Fly list can effectively bar someone from traveling internationally. Analyzing the deprivation in this manner might point toward finding the deprivation of a significant liberty interest. In contrast, one might characterize placement on a No Fly list as limited to a restriction on a person's "preferred method of travel," rather than the ability to travel at all. In litigation concerning the No Fly list, the DOJ has argued that "[t]he Constitution does not guarantee ... a right to the most convenient means of travel, nor does it create a liberty interest in travel by airplane in particular." Following this line of argument, because a person on the No Fly list is not barred from travel entirely, the deprivation is of a less significant liberty interest. A court would next examine the risk of an erroneous deprivation of liberty under the current procedural framework and the potential value of imposing additional procedures on the process. Put another way, a court would investigate how likely it is that someone would be incorrectly placed on the No Fly list, and how helpful requiring different procedures would be in preventing such errors. In analyzing the risk of error, a court might examine both the standard used by the government to make its initial decision to place someone on the No Fly list, as well as the procedures currently afforded travelers via DHS TRIP, including its judicial review provision. One factor courts examine in weighing the risk of error is the amount of discretion afforded the decisionmaker. For example, the Supreme Court has distinguished between a deprivation based on a medical assessment and one predicated on a variety of disparate information including "witness credibility and veracity." For the Court, the latter situation involves a greater risk of error than the former. Another factor might be the standard of proof required for the government to deprive someone of liberty. For example, the Court has held that before a state may permanently sever a parent's relation with a child, a state must meet a higher evidentiary threshold than "fair preponderance of the evidence." Yet another factor is the ability to see and challenge the evidence relied on to justify a deprivation. In the context of a security clearance revocation that resulted in the impairment of a plaintiff's job opportunities, the Supreme Court stressed that "where governmental action seriously injures an individual, and the reasonableness of the action depends on fact findings, the evidence used to prove the Government's case must be disclosed to the individual so that he has an opportunity to show that it is untrue." Likewise, in the disability benefits context, the Court has noted the important "safeguard against mistake" of permitting access to the government's information and the reasons for the government's action, as well as the ability of a claimant to submit his own arguments and challenge the accuracy of the government's conclusion. Finally, in the context of considering the government's detention of a U.S. citizen in an armed conflict, the Supreme Court has ruled that a process where "the Executive's factual assertions go wholly unchallenged or are simply presumed correct without any opportunity ... to demonstrate otherwise falls constitutionally short." When a "citizen-detainee ... challenge[s] his classification as an enemy combatant [he] must receive fair notice of the factual basis for his classification, and a fair opportunity to rebut the Government's factual assertions before a neutral decisionmaker." Some plaintiffs who have challenged their alleged placement on the No Fly list have argued both that the current standard used to place someone on a No Fly list entails a high risk of error, and that the current procedure afforded those seeking to challenge their placement on the No Fly list creates a high risk of an erroneous deprivation. There is arguably a considerable amount of discretion involved in making the determination that someone is a danger to aviation safety. In addition, a traveler does not have the opportunity to evaluate the evidence against her or to present her own evidence to correct the record before placement on the list. Some courts have noted government studies that document numerous errors with the operation of the watch lists; and media accounts have highlighted mistaken placements on the No Fly list. The executive branch has argued, however, that such studies predate the current methods used under the Secure Flight program, which has reduced the number of travelers wrongly denied boarding. In addition, DHS TRIP does provide a redress process, which can be appealed to a United States court of appeals. One might argue that this opportunity for judicial review of the agency's determination is sufficient to prevent erroneous deprivations. Finally, a court would examine the government's interest in the matter and the cost of imposing additional procedures. The government has a strong interest in preventing terrorism, which includes ensuring the safety of air travel. The operation of the No Fly list arguably is an important tool to do so. The government also has an interest in protecting sensitive national security information. The executive branch has argued that "protecting TSDB information enables agencies to share that information across the government, without fear that it will be disclosed whenever anyone sues after he or she cannot travel as he or she might choose." Requiring DHS to reveal classified information through this process, even to the complainant, could "damage ... national security, including by jeopardizing intelligence sources and methods." Accordingly, the danger to the public of disclosing certain material might, in some observers' view, outweigh the benefit to the plaintiff. Indeed, the executive branch has argued that "opportunities for confrontation and rebuttal are not absolute requirements of due process, particularly where the information upon which the government acts is highly sensitive." More generally, courts have sometimes been reluctant to require the executive branch to release information that implicates national security concerns. In cases bringing procedural due process claims that concern sensitive materials outside of No Fly list challenges, courts have often declined to require the government to release classified information directly to the plaintiff. Nonetheless, as explained below, at least one federal district court—in ruling on a challenge to placement on the No Fly list—has signaled that permitting a plaintiff's counsel with proper security clearances to access the government's evidence might alleviate some national security concerns. However, in contexts outside of challenges to the No Fly list, some courts have declined to interpret this possibility as foreclosing the government's interest in protecting national security. As the Seventh Circuit reasoned in a 2014 ruling, counsel might, "in their zeal to defend their client ... inadvertently say things that would provide clues to classified material." In contrast, other courts, including the Ninth Circuit, have approved this procedure, at least in certain circumstances. Finally, one alternative used in other national security contexts is a requirement that the government provide unclassified summaries of particular information to a plaintiff, rather than the classified material itself. In addition, specific forms of procedural protections might compromise national security more than others. A requirement that the government provide prior notice to anyone placed on a No Fly list and a pre-deprivation hearing where both sides presented evidence might "aid terrorists in their plans to bomb and kill Americans" by providing advance notice to all suspected terrorists. More generally, the Supreme Court has recognized that a pre-deprivation hearing is not necessary in certain situations, for example, those implicating substantial national security concerns or public safety. Judicial resolution of a due process challenge requires a balancing of all three factors to determine what process is due. Several federal district courts directly addressed challenges to placement on the No Fly list which alleged that the government's prior redress procedures violated due process. In a case in the Northern District of California, a federal court ruled on a claim brought by Rahinah Ibrahim, a Malaysian national who was present in the United States under a student visa in 2005, when she was prevented from boarding a plane to Malaysia and temporarily detained for several hours. During the trial, the government admitted that it had mistakenly placed her on the No Fly list. The court ruled that when the government mistakenly places someone on a No Fly list, due process "requires the government to cleanse and/or correct its lists and records of the mistaken information and to certify under oath that such correction(s) have been made." In addition to ordering this remedy, the judge also directed the government to reveal to the plaintiff whether she was currently on the No Fly list. At least in this situation, the court ruled, where a plaintiff is mistakenly placed on the No Fly list, the current redress procedures under DHS TRIP did not satisfy due process. However, the scope of the ruling is rather narrow. The court explained that its ruling was limited to a situation where the government admits that it has mistakenly placed a traveler on the list. The court left open situations where the government had not conceded error. In contrast, at least two federal district courts have ruled that the government's procedures under the prior DHS TRIP process violated due process in a case where the government did not appear to concede error. In Latif v. Holder , for example, the plaintiffs had been barred from flying and submitted complaints via the prior DHS TRIP process; pursuant to the procedures described above, the government's reply did not confirm or deny whether they were on a No Fly list or provide any reason why plaintiffs could not board an aircraft. The court found that the plaintiffs had "constitutionally-protected liberty interests in traveling internationally by air, which are significantly affected by being placed on the No-Fly list." The court conducted a Mathews balancing test and concluded that the DHS TRIP process failed to provide due process. The court noted the various harms that can result from being denied boarding on international flights and concluded that the deprivation was "significant." Turning to the second Mathews factor, the court noted a "fundamental flaw" of the procedures in both the DHS TRIP and judicial review process: a low evidentiary standard—reasonable suspicion—sufficient to be placed on the No Fly list, combined with a one sided review process. Taken together, the court found, these aspects made it likely that factual errors in the government's record could go uncorrected. Therefore, the court concluded, the government's procedures "contain[ed] a high risk of erroneous deprivation" of the plaintiffs' liberty interests. Further, the court found, providing notice of inclusion on the list, a list of reasons for placement on the list, and/or the opportunity to present exculpatory evidence "would have significant probative value in ensuring that individuals are not erroneously deprived of their constitutionally-protected liberty interests." On the other hand, the court recognized the significant government interest in national security, the third Mathews factor. Nonetheless, the court noted that certain procedural protections were possible that did not endanger national security, such as providing summaries of classified information or permitting defense counsel with appropriate clearances to access sensitive material. Consequently, the court held that "the absence of any meaningful procedures" to contest plaintiffs' placement on the No Fly list violated due process. The court ordered the government to "fashion new procedures" that satisfied due process, including notifying the plaintiffs whether or not they were on the No Fly list and "the reasons for placement on that List." That notice must be sufficient to provide the plaintiffs with a meaningful opportunity to respond, and that response must be taken into account at both the judicial and administrative review stages. However, the court left the precise type of procedures up to the government and allowed for the possibility that such disclosure might "create an undue risk to national security." That determination, however, had to be made on a case-by-case basis. As mentioned above, the government has revised the procedures at issue in the cases discussed above. The adequacy of the new DHS TRIP redress process has also been challenged as violating the Due Process Clause. In a case before the U.S. District Court for the Eastern District of Virginia, after largely adopting the analysis of the court in Latif v. Holder and ruling that the prior DHS TRIP procedures violated due process, the court rejected the plaintiff's motion for summary judgment regarding the revised procedures. The court observed that because the plaintiff had not undergone review under the revised procedures, it could not decide on the current record whether the new process complied with the Due Process Clause. The court did note, however, that "as described to the Court," the new procedures "appear to allow for both a constitutionally adequate post-deprivation review and also a reviewing court to be presented with an administrative record that allows a sufficient assessment concerning whether" the plaintiff was "given a constitutionally adequate opportunity to challenge any placement on the No Fly List." In a footnote, the court observed that "[s]ubstantial issues exist concerning whether and in what form DHS TRIP adequately provides for judicial review of a decision to place someone on the No Fly List," but declined to address these issues in the immediate matter before it. Following the adverse ruling against the government in Latif v. Holder in 2014, the government reconsidered the DHS TRIP petitions and applied revised procedures to the plaintiffs in the case. The government then disclosed that seven of the plaintiffs were not on the No Fly list, but the TSA Administrator decided that six others should remain. Subsequently, in Latif v. Lynch , those remaining plaintiffs moved for summary judgment, claiming that the revised procedures violated due process. The court first ruled that due process does not mandate the use of a "clear and convincing" standard to place individuals on the No Fly list—the standard used in deportation and civil commitment cases. Instead, use of the "reasonable suspicion" standard is appropriate because the deprivation of liberty interest in placement on the No Fly list is less severe. In addition, the court reiterated its earlier conclusion that due process required that the government provide the plaintiffs with reasons for placement on the list sufficient to permit them to respond meaningfully. The court held that the revised DHS TRIP procedures appeared on their face to satisfy this standard because the notice sent to the plaintiffs provided an unclassified summary of the reasons they were placed on the list. However, the court ruled that it could not yet decide whether the disclosure to each individual plaintiff was sufficient as the record did not indicate what information was withheld or the reasons for any withholding. Likewise, the court held that due process did not require the government to release classified information or the actual evidence underlying its decision to place plaintiffs on the No Fly list. The court explained that revised DHS TRIP procedures appeared on their face to satisfy the requirement that the government provide sufficient information to permit the plaintiffs to respond meaningfully, but the record was not sufficiently developed to decide the adequacy of the disclosures made to the specific plaintiffs. Further, the court concluded that the lack of a live hearing with an opportunity to cross-examine witnesses did not violate due process. The court noted that similar procedures have been approved in the context of government designations of entities as Specially Designated Global Terrorists. While the private interest in those situations is a property interest, rather than a liberty interest deprivation as in No Fly list cases, the court found the weight of the two interests to be substantially similar. Because of the important national security concerns at issue, a document based hearing is sufficient to satisfy due process. Finally, the court concluded that "to the extent that Defendants withhold information" from plaintiffs for national security reasons, the government "must implement procedures to minimize the amount of material information withheld." When appropriate, the government must provide unclassified summaries of relevant materials "and/or whether additional disclosures can be made to Plaintiffs' counsel who have the appropriate security clearances." On the record before it, however, the court could not determine whether this standard was met for each plaintiff. As explained above, some travelers have challenged their alleged placement on the No Fly list and the government's redress process in federal court outside of the DHS TRIP review mechanism. However, governmental privileges barring disclosure of sensitive information present hurdles for plaintiffs. In No Fly list cases brought in federal courts, a number of common law and statutory privileges have been invoked by the government to bar a plaintiff's access to certain information via discovery, including the state secrets, law enforcement, and deliberative process privileges. When properly invoked and accepted by courts, these privileges can prevent plaintiffs from examining certain sensitive information potentially relevant to their case, potentially impeding their ability to challenge placement on the list. For example, the state secrets privilege is an evidentiary privilege that allows the government to withhold information during civil litigation if there is a reasonable danger that disclosure would endanger national security. If the government invokes the privilege during litigation, the court will then make an independent determination of the validity of the claim, possibly via in camera review of the relevant materials. If the court is satisfied that the privilege applies, that information will be unavailable to the plaintiff. For example, in a 2015 case challenging a plaintiff's placement on the No Fly list, the government invoked the state secrets privilege and moved to dismiss the case entirely. The government claimed that the privilege applied both to the "sensitive policies and procedures used in the watchlisting process" and any substantive underlying information regarding the reasons for placement on the No Fly list. According to the government, this precluded any consideration of the adequacy of the redress process, as well as a full inquiry into "the possibility of substitute procedures." Indeed, "any attempt to litigate how these nomination procedures were applied in this case ... risks disclosure of the privileged information." In addition, the government argued that due to the potential for sensitive matters to be probed via discovery, "future proceedings will inherently put the privileged information at risk of being disclosed." Accordingly, the government moved to dismiss the case entirely. This motion to dismiss was denied by the court, on the grounds that the plaintiff's claim might be adjudicated without recourse to documents subject to the privilege. The law enforcement privilege has also been invoked by the government in challenges to placement on the No Fly list. The purpose of the privilege is "to prevent disclosure of law enforcement techniques and procedures, to preserve the confidentiality of sources, to protect witnesses and law enforcement personnel, to safeguard the privacy of individuals involved in an investigation, and otherwise to prevent interference with an investigation." The investigation is not required to be ongoing, as disclosure of past tactics might impair future investigations. However, the privilege is not absolute: "[t]he public interest in nondisclosure must be balanced against the need of a particular litigant for access to the privileged information." In order to conduct this balancing test, courts often examine an extensive list of factors. Courts may examine the evidence in camera in order to determine if the privilege applies and balance the litigant's need against the public interest in nondisclosure. If a court determines that the privilege applies, then that information will not be available to the defendant. In No Fly list cases, the executive branch has asserted this privilege over a "plaintiff's status on any terrorist database and the policies and procedures used for determining how an individual's name is placed in such a database." Similarly, the deliberative process privilege has been invoked by the executive branch in challenges to placement on the No Fly list. The privilege allows the government to withhold material that "reflect[] advisory opinions, recommendations and deliberations comprising part of a process by which governmental decisions and policies are formulated." In order to qualify, documents must be "predecisional" and "deliberative." A document qualifies as the former if it "was prepared in order to assist an agency decisionmaker in arriving at his decision," and the latter if its release would "expose an agency's decisionmaking process in such a way as to discourage candid discussion within the agency and thereby undermine the agency's ability to perform its functions." As with the other privileges, however, its invocation by the government is not absolute. A plaintiff "may obtain deliberative materials if his or her need for the materials and the need for accurate fact-finding over-ride the government's interest in non-disclosure." In the No Fly list context, this privilege might be invoked in an attempt to withhold documents used in certain decision-making processes, such as whether to place an individual on the No Fly list. Finally, TSA has statutory discretion to designate certain material as "sensitive security information," or "information obtained ... in the conduct of security activities ... the disclosure of which TSA has determined would ... [b]e detrimental to the security of transportation." Such information is "not available for public inspection," and the government has claimed exemptions from disclosure at trial on this basis. Nonetheless, as with the privileges discussed above, plaintiffs and their counsel can access information in certain circumstances. Properly balancing the important national security interest of preventing terrorist attacks with the civil liberties of travelers prevented from boarding a plane is a complicated and delicate matter. Operation of the government's No Fly list implicates a wide variety of statutory and constitutional issues. A number of lower courts have ruled that a previous version of the government's redress procedures was unconstitutional. While the government's revised framework is currently the subject of further litigation, initial rulings have generally taken a more favorable view of the constitutionality of the revised process.

Summary: In order to protect national security, the government maintains various terrorist watchlists, including the "No Fly" list, which contains the names of individuals to be denied boarding on commercial airline flights. Travelers on the No Fly list are not permitted to board an American airline or any flight on a foreign air carrier that lands or departs from U.S. territory or flies over U.S. airspace. Some individuals have claimed that their alleged placement on the list was the result of an erroneous determination by the government that they posed a national security threat. In some cases, it has been reported that persons have been prevented from boarding an aircraft because they were mistakenly believed to be on the No Fly list, sometimes on account of having a name similar to another person who was actually on the list. As a result, various legal challenges to placement on the list have been brought in court. The Due Process Clause of the Constitution provides that no person shall be "deprived of life, liberty, or property, without due process of law." Accordingly, when the government deprives someone of a constitutionally protected liberty interest, it must follow certain procedures. Several courts have found that placement on the No Fly list may impair constitutionally protected interests, including the right to travel internationally, and that the government's redress procedures must therefore satisfy due process. Typically, due process requires that the government provide a person with notice of the deprivation and an opportunity to be heard before a neutral party. However, the requirements of due process are not fixed, and can vary according to relevant factors. When determining the proper procedural protections in a given situation, courts employ the balancing test articulated by the Supreme Court in Mathews v. Eldridge, which weighs the private interests affected against the government's interest. Courts applying this balancing test might consider several factors, including the severity of the deprivation involved in placement on the No Fly list. In addition, courts may examine the risk of an erroneous deprivation under the current procedural framework and the potential value of imposing additional procedures on the process. Finally, courts may inquire into the government's interest in preserving the status quo, including the danger of permitting plaintiffs to access sensitive national security information. The government has established a redress process—known as DHS TRIP—for individuals who wish to challenge their treatment at transportation hubs. A prior version of these procedures was found by a number of courts to violate the Due Process Clause. The government has since revised DHS TRIP, although these new procedures are also being challenged in federal court. Litigation is further complicated by several legal issues, such as the state secrets privilege, that can bar plaintiffs from accessing certain information during litigation.