opinion: Justice Marshall
  delivered the opinion of the Court.
  Section 340 (a) of the Immigration and Nationality Act of 1952, 66 Stat. 260, as amended, 8 U. S. C. § 1451 (a), requires revocation of United States citizenship that was “illegally procured or . . . procured by concealment of a material fact or by willful misrepresentation.” The Government brought this denaturalization action, alleging that petitioner procured his citizenship illegally or by willfully misrepresenting a material fact. The District Court entered judgment for petitioner, but the Court of Appeals reversed and ordered entry of a judgment of denaturalization. We granted certiorari, 444 U. S. 1070, to resolve two questions: whether petitioner’s failure to disclose, in his application for a visa to come to this country, that he had served during the Second World War as an armed guard at the Nazi concentration camp at Treblinka, Poland, rendered his citizenship revocable as “illegally procured” or procured by willful misrepresentation of a material fact, and if so, whether the District Court nonetheless possessed equitable discretion to refrain from entering judgment in favor of the Government under these circumstances.
  I
  A
  Petitioner was born in the Ukraine in 1907. He was drafted into the Russian Army in June 1941, but was captured by the Germans shortly thereafter. After being held in a series of prisoner-of-war camps, petitioner was selected to go to the German camp at Travnicki in Poland, where he received training as a concentration camp guard. In September 1942, he was assigned to the Nazi concentration camp at Treblinka in Poland, where he was issued a uniform and rifle and where he served as a guard during 1942 and 1943. The infamous Treblinka concentration camp was described by the District Court as a “human abattoir” at which several hundred thousand Jewish civilians were murdered. After an armed uprising by the inmates at Treblinka led to the closure of the camp in August 1943, petitioner was transferred to a German labor camp at Danzig and then to the German prisoner-of-war camp at Poelitz, where he continued to serve as an armed guard. Petitioner was eventually transferred to Hamburg where he served as a warehouse guard. Shortly before the British forces entered that city in 1945, petitioner discarded his uniform and was able to pass as a civilian. For the next four years, he worked in Germany as a laborer.
  B
  In 1948, Congress enacted the Displaced Persons Act (DPA or Act), 62 Stat. 1009, to enable European refugees driven from their homelands by the war to emigrate to the United States without regard to traditional immigration quotas. The Act’s definition of “displaced persons” eligible for immigration to this country specifically excluded individuals who had “assisted the enemy in persecuting civil [ians]” or had “voluntarily assisted the enemy forces ... in their operations . ...” Section 10 of the DPA, 62 Stat. 1013, placed the burden of proving eligibility under the Act on the person seeking admission and provided that “[a]ny person who shall willfully make a misrepresentation for the purpose of gaining admission into the United States as an eligible displaced person shall thereafter not be admissible into the United States.” The Act established an elaborate system for determining eligibility for displaced person status. Each applicant was first interviewed by representatives of the International Refugee Organization of the United Nations (IRO) who ascertained that the person was a refugee or displaced person. The applicant was then interviewed by an official of the Displaced Persons Commission, who made a preliminary determination about his eligibility under the DPA. The final decision was made by one of several State Department vice consuls, who were specially trained for the task and sent to Europe to administer the Act. Thereafter, the application was reviewed by officials of the Immigration and Naturalization Service (INS) to make sure that the applicant was admissible into the United States under the standard immigration laws.
  In October 1949, petitioner applied for admission to the United States as a displaced person. Petitioner falsified his visa application by lying about his wartime activities. He told the investigators from the Displaced Persons Commission that he had been a farmer in Sarny, Poland, from 1937 until March 1942, and that he had then been deported to Germany and forced to work in a factory in Poelitz until the end of the war, when he fled to Hamburg. Petitioner told the same story to the vice consul who reviewed his case and he signed a sworn statement containing these false representations as part of his application for a DPA visa. Petitioner’s false statements were not discovered at the time and he was issued a DPA visa, and sailed to the United States where he was admitted for permanent residence. He took up residence in Connecticut and for three decades led an uneventful and law-abiding life as a factory worker.
  In 1969, petitioner applied for naturalization at the INS office in Hartford, Conn. Petitioner did not disclose his wartime service as a concentration camp armed guard in his application, and he did not mention it in his sworn testimony to INS naturalization examiners. The INS examiners took petitioner’s visa papers at face value and recommended that his citizenship application be granted. On this recommendation, the Superior Court of New Haven County granted his petition for naturalization and he became an American citizen on April 23,1970.
  C
  Seven years later, after petitioner had moved to Miami Beach and become a resident of Florida, the Government filed this action in the United States District Court for the Southern District of Florida to revoke petitioner’s citizenship. The complaint alleged that petitioner should have been deemed ineligible for a DPA visa because he had served as an armed guard at Treblinka and had committed crimes or atrocities against inmates of the camp because they were Jewish. The Government charged that petitioner had willfully concealed this information both in applying for a DPA visa and in applying for citizenship, and that therefore petitioner had procured his naturalization illegally or by willfully misrepresenting material facts.
  The Government’s witnesses at trial included six survivors of Treblinka who claimed that they had seen petitioner commit specific acts of violence against inmates of the camp. Each witness made a pretrial identification of petitioner from a photo array that included his 1949 visa photograph, and three of the witnesses made courtroom identifications. The Government also called as a witness Kempton Jenkins, a career foreign service officer who served in Germany after the war as one of the vice consuls who administered the DPA. Jenkins had been trained to administer the Act and had reviewed some 5,000 visa applications during his tour of duty. Record 711-714, 720-722. Without objection from petitioner, Jenkins was proffered by the Government and accepted by the court, as an expert witness on the interpretation and application of the DPA. Id., at 719-721, 726-727, 734.
  Jenkins testified that the vice consuls made the final decision about an applicant’s eligibility for displaced person status. He indicated that if there had been any suggestion that an applicant “had served or been involved in” a concentration camp, processing of his application would have been suspended to permit a thorough investigation. Id., at 766. If it were then determined that the applicant had been an armed guard at the camp, he would have been found ineligible for a visa as a matter of law. Id., at 767-768, 822. Jenkins explained that service as an armed guard at a concentration camp brought the applicant under the statutory exclusion of persons who “assisted the enemy in persecuting civil [ians],” regardless of whether the applicant had not volunteered for service or had not committed atrocities against inmates. Id., at 768, 797-798. Jenkins emphasized that this interpretation of the Act was “uniformly” accepted by the vice consuls, and that furthermore, he knew of no case in which a known concentration camp guard was found eligible for a DPA visa. Id., at 767. Jenkins also described the elaborate system that was used to screen visa applicants and he testified that in interviewing applicants, the vice consuls bent over backwards in interrogating each person to make sure the applicant understood what he was doing. Id., at 746.
  Petitioner took the stand in his own behalf. He admitted his service as an armed guard at Treblinka and that he had known that thousands of Jewish inmates were being murdered there. Id., at 1442, 1461-1452, 1465. Petitioner claimed that he was forced to serve as a guard and denied any personal involvement in the atrocities committed at the camp, id., at 1276, 1297-1298, 1539-1540; he insisted that he had merely been a perimeter guard. Petitioner admitted, however, that he had followed orders and shot in the general direction of escaping inmates during the August 1943 uprising that led to closure of the camp. Id., at 1507-1509, 1546, 1564. Petitioner maintained that he was a prisoner of war at Treblinka, id., at 1495, although he admitted that the Russian armed guards significantly outnumbered the German soldiers at the camp, that he was paid a stipend and received a good service stripe from the Germans, and that he was allowed to leave the camp regularly but never tried to escape. Id., at 1467-1471, 1489-1494, 1497, 1508. Finally, petitioner conceded that he deliberately gave false statements about his wartime activities to the investigators from the Displaced Persons Commission and to the vice consul who reviewed his visa application. Id., at 1518-1524.
  The District Court entered judgment in favor of petitioner. 455 F. Supp. 893 (1978). The court found that petitioner had served as an armed guard at Treblinka and that he lied about his wartime activities when he applied for a DPA visa in 1949. The court, found, however, that petitioner was forced to serve as a guard. The court concluded that it could credit neither the Treblinka survivors’ identification of petitioner nor their testimony, and it held that the Government had not met its burden of proving that petitioner committed war crimes or atrocities at Treblinka.
  Turning to the question whether petitioner’s false statements about his activities during the war were misrepresentations of “material” facts, the District Court, relying on our decision in Chaunt v. United States, 364 U. S. 350 (1960), held that the Government had to prove
  “that either (1) facts were suppressed ‘which, if known, would have warranted denial of citizenship’ or (2) that their disclosure ‘might have been useful in an investigation possibly leading to the discovery of other facts warranting denial of citizenship.’ ” 455 F. Supp., at 915 (quoting 364 U. S., at 355).
  The District Court rejected the Government’s claim that disclosure of petitioner’s service as a concentration camp armed guard would have been grounds for denial of citizenship. The court therefore ruled that the withheld facts were not material under the first Chaunt test. The Government argued, however, that the second Chaunt test did not require proof that the concealed facts prevented an investigation that would have revealed facts warranting denial of citizenship. The Government contended instead that the second test merely required proof that an investigation might have uncovered such facts and it argued that petitioner’s concealment of his service at Treblinka fell within this test. The District Court conceded that the language of Chaunt was ambiguous enough to support the Government’s interpretation of the second test. But relying on decisions-by the United States Courts of Appeals for the Third and Ninth Circuits, the District Court rejected the Government’s position and interpreted both Chaunt tests as requiring proof that “the true facts would have warranted denial of citizenship.” 455 F. Supp., at 916. Applying this test, the court ruled that petitioner’s false statements were not “material” within the meaning of the denaturalization statute. In doing so, the court first rejected Jenkins’ testimony and held that petitioner was not ineligible for a DPA visa. The court concluded that petitioner did not come under the DPA’s exclusion of persons who had assisted in the persecution of civilians because he had served involuntarily. Second, the court found that although disclosure of petitioner’s service as a Treblinka guard “certainly would” have prompted an investigation into his activities, the Government had failed to prove that such an inquiry would have uncovered any additional facts warranting denial of petitioner’s application for a visa.. Id., at 916.
  As an alternative basis for its decision, the District Court held that even assuming that petitioner had misrepresented “material” facts, equitable and mitigating circumstances required that petitioner be permitted to retain his citizenship. Specifically, the court relied on its finding that the evidence that petitioner had committed any war crimes or atrocities at Treblinka was inconclusive, as well as the uncontroverted evidence that he had been responsible and law-abiding since coming to the United States. The District Court suggested that this Court had not previously considered the question whether a district court has discretion to consider the equities in a denaturalization ' case. The court reasoned that since naturalization courts have considered the equities in determining whether citizenship should be granted, similar discretion should also be available in denaturalization proceedings.
  The Court of Appeals for the Fifth Circuit reversed and remanded the case with instructions to enter judgment for the Government and to cancel petitioner’s certificate of citizenship. 597 F. 2d 946 (1979). Although the Court of Appeals agreed with the District Court that Chaunt was controlling on the question of the materiality of petitioner’s false statements, it disagreed with the District Court’s interpretation of the second Chaunt test as requiring proof of ultimate facts warranting denial of citizenship. Instead, the Court of Appeals agreed with the Government that the second Chaunt test requires only clear and convincing proof that (a) disclosure of the true facts would have led to an investigation and (b) the investigation might have uncovered other facts warranting denial of citizenship.
  In applying its formulation of the second Chaunt test to the facts of the case, the Court of Appeals concluded that one part of the test was satisfied by the District Court’s finding that the American authorities would have conducted an investigation if petitioner had disclosed that he had served as an armed guard at Treblinka. The Court of Appeals then found that Jenkins’ testimony and other evidence before the District Court clearly and convincingly proved that the investigation might have resulted in denial of petitioner’s application for a visa and the Court of Appeals held that petitioner procured his naturalization “by misrepresentation and concealment of his whereabouts during the war years and his service as a concentration camp guard.” 597 F. 2d, at 953. The Court of Appeals further held that the District Court had erred in supposing that it had discretion to enter judgment in favor of petitioner notwithstanding a finding that petitioner had procured his naturalization by willfully concealing material facts. The Court of Appeals concluded that “[t]he denaturalization statute . . . does not accord the district courts any authority to excuse the fraudulent procurement of citizenship.” Id., at 954. Accordingly, the Court of Appeals held that petitioner’s citizenship must be revoked. We affirm, but for reasons which differ from those stated by the Court of Appeals.
  II
  Our examination of the questions presented by this case must proceed within the framework established by two lines of prior decisions of this Court that may, at first blush, appear to point in different directions.
  On the one hand, our decisions have recognized that the right to acquire American citizenship is a precious one, and that once citizenship has been acquired, its loss can have severe and unsettling consequences. See Costello v. United States, 365 U. S. 265, 269 (1961); Chaunt v. United States, 364 U. S., at 353; Baumgartner v. United States, 322 U. S. 665, 675-676 (1944); Schneiderman v. United States, 320 U. S. 118, 122 (1943). For these reasons, we have held that the Government “carries a heavy burden of proof in a proceeding to divest a naturalized citizen of his citizenship.” Costello v. United States, supra, at 269. The evidence justifying revocation of citizenship must be “ 'clear, unequivocal, and convincing’ ” and not leave “ 'the issue in doubt.’ ” Schneiderman v. United States, supra, at 125 (quoting Maxwell Land-Grant Case, 121 U. S. 325, 381 (1887)). Any less exacting standard would be inconsistent with the importance of the right that is at stake in a denaturalization proceeding. And in reviewing denaturalization cases, we have carefully examined the record ourselves. See, e. g., Costello v. United States, supra; Chaunt v. United States, supra; Nowak v. United States, 356 U. S. 660 (1958); Baumgartner v. United States, supra.
  At the same time, our cases have also recognized that there must be strict compliance with all the congressionally imposed prerequisites to the acquisition of citizenship. Failure to comply with any of these conditions renders the cértificate of citizenship “illegally procured,” and naturalization that is unlawfully procured can be set aside. 8 U. S. C. § 1451 (a); Afroyim v. Rusk, 387 U. S. 253, 267, n. 23 (1967). See Maney v. United States, 278 U. S. 17 (1928); United States v. Ness, 245 U. S. 319 (1917); United States v. Ginsberg, 243 U. S. 472 (1917). As we explained in one of these prior decisions:
  “An alien who seeks political rights as a member of this Nation can rightfully obtain them only upon terms and conditions specified by Congress. . . .
  “No alien has the slightest right to naturalization unless all statutory requirements are complied with; and every certificate of citizenship must be treated as granted upon condition that the government may challenge it . . . and demand its cancellation unless issued in accordance with such requirements.” United States v. Ginsberg, supra, at 474-475.
  This judicial insistence on strict compliance with the statutory conditions precedent to naturalization is simply an acknowledgment of the fact that Congress alone has the constitutional authority to prescribe rules for naturalization, and the courts’ task is to assure compliance with the particular prerequisites to the acquisition of United States citizenship by naturalization legislated to safeguard the integrity of this “priceless treasure.” Johnson v. Eisentrager, 339 U. S. 763, 791 (1950) (Black, J., dissenting).
  Thus, what may at first glance appear to be two inconsistent lines of cases actually reflect our consistent recognition of the importance of the issues that are at stake — for the citizen as well as the Government — in a denaturalization proceeding. With this in mind, we turn to petitioner’s contention that the Court of Appeals erred in reversing the judgment of the District Court.
  Ill
  Petitioner does not and, indeed, cannot challenge the Government’s contention that he willfully misrepresented facts about his wartime activities when he applied for a DPA visa in 1949. Petitioner admitted at trial that he “willingly” gave false information in connection with his application for a DPA visa so as to avoid the possibility of repatriation to the Soviet Union. Record 1520. The District Court specifically noted that there was no dispute that petitioner “lied” in his application. 455 F. Supp., at 914. Thus, petitioner falls within the plain language of the DPA’s admonition that “[a]ny person who shall willfully make a misrepresentation for the purposes of gaining admission into the United States as an eligible displaced person shall thereafter not be admissible into the United States.” 62 Stat. 1013. This does not, however, end our inquiry, because we agree with the Government that this provision only applies to willful misrepresentations about “material” facts. The first issue we must examine then, is whether petitioner’s false statements about his activities during the war, particularly the concealment of his Treblinka service, were "material.”
  A
  At the outset, we must determine the proper standard to be applied in judging whether petitioner’s false statements were material. Both petitioner and the Government have assumed, as did the District Court and the Court of Appeals, that materiality under the above-quoted provision of the DP A is governed by the standard announced in Chaunt v. United States, 364 U. S. 350 (1960). But we do not find it so obvious that the Chaunt test is applicable here. In that case, the Government charged that Chaunt had procured his citizenship by concealing and misrepresenting his record of arrests in the United States in his application for citizenship, and that the arrest record was a “material” fact within the meaning of the denaturalization statute. Thus, the materiality standard announced in that case pertained to false statements in applications for citizenship, and the arrests that Chaunt failed to disclose all took place after he came to this country. The case presented no question concerning the lawfulness of his initial entry into the United States.
  In the instant case, however, the events on which the Government relies in seeking to revoke petitioner’s citizenship took place before he came to this country and the Government is seeking to revoke petitioner’s citizenship because of the alleged unlawfulness of his initial entry into the United States. Although the complaint charged that petitioner misrepresented facts about his wartime activities in both his application for a visa and his application for naturalization, both the District Court and the Court of Appeals focused on the false statements in petitioner’s application for a visa. Thus, under the analysis of both the District Court and the Court of Appeals, the misrepresentation that raises the ma-terality issue in this case was contained in petitioner’s application for a visa. These distinctions plainly raise the important question whether the Chaunt test for materiality of misrepresentations in applications for citizenship also applies to false statements in visa applications.
  It is, of course, clear that the materiality of a false statement in a visa application must be measured in terms of its effect on the applicant’s admissibility into this country. See United States v. Rossi, 299 F. 2d 650, 652 (CA9 1962). At the very least, a misrepresentation must be considered material if disclosure of the true facts would have made the applicant ineligible for a visa. Because we conclude that disclosure of the true facts about petitioner’s service as an armed guard at Treblinka would, as a matter of law, have made him ineligible for a visa under the DP A, we find it unnecessary to resolve the question whether Chaunt’s materiality test also governs false statements in visa applications.
  Section 2 (b) of the DPA, 62 Stat. 1009, by incorporating the definition of “[p]ersons who will not be [considered displaced persons]” contained in the Constitution of the IR.O, see n. 3, supra, specifically provided that individuals who “assisted the enemy in persecuting civil [ians]” were ineligible for visas under the Act. Jenkins testified that petitioner’s service as an armed guard at a concentration camp — whether voluntary or not — made him ineligible for a visa under this provision. Jenkins’ testimony was based on his firsthand experience as a vice consul in Germany after the war reviewing DPA visa applications. Jenkins also testified that the practice of the vice consuls was to circulate among the other vice consuls the case files of any visa applicant who was shown to have been a concentration camp armed guard. Record 826. Thus, Jenkins and the other vice consuls were particularly well informed about the practice concerning the eligibility of former camp guards for DPA visas. The District Court evidently agreed that a literal interpretation of the statute would confirm the accuracy of Jenkins’ testimony. 455 F. Supp., at 913. But by construing § 2 (a) as only excluding individuals who voluntarily assisted in the persecution of civilians, the District Court was able to ignore Jenkins’ uncontroverted testimony about how the Act was interpreted by the officials who administered it.
  The Court of Appeals evidently accepted the District Court’s construction of the Act since it agreed that the Government had failed to show that petitioner was ineligible for a DP A visa. 597 F. 2d, at 953. Because we are unable to find any basis for an “involuntary assistance” exception in the language of § 2 (a), we conclude that the District Court’s construction of the Act was incorrect. The plain language of the Act mandates precisely the literal interpretation that the District Court rejected: an individual’s service as a concentration camp armed guard — whether voluntary or involuntary- — made him ineligible for a visa. That Congress was perfectly capable of adopting a “voluntariness” limitation where it felt that one was necessary is plain from comparing § 2 (a) with § 2 (b), which excludes only those individuals who “voluntarily assisted the enemy forces ... in their operations . . . .” Under traditional principles of statutory construction, the deliberate omission of the word “voluntary” from § 2 (a) compels the conclusion that the statute made all those who assisted in the persecution of civilians ineligible for visas. See National Railroad Passenger Corp. v. National Assn, of Railroad Passengers, 414 U. S. 453, 458 (1974); Botany Worsted Mills v. United States, 278 U. S. 282, 289 (1929). As this Court has previously stated: “We are not at liberty to imply a condition which is opposed to the explicit terms of the statute. ... To [so] hold ... is not to construe the Act but to amend it.” Detroit Trust Co. v. The Thomas Barium, 293 U. S. 21, 38 (1934). See FTC v. Sun Oil Co., 371 U. S. 505, 514-515 (1963). Thus, the plain language of the statute and Jenkins’ uncontradicted and unequivocal testimony leave no room for doubt that if petitioner had disclosed the fact that he had been an armed guard at Treblinka, he would have been found ineligible for a visa under the DPA. This being so, we must conclude that petitioner’s false statements about his wartime activities were “willfu[l] [and material] misrepresentation [s] [made] for the purpose of gaining admission into the United States as an eligible displaced person.” 62 Stat. 1013. Under the express terms of the statute, petitioner was “thereafter not . . . admissible into the United States.” Ibid.
  Our conclusion that petitioner was, as a matter of law, ineligible for a visa under the DPA makes the resolution of this case fairly straightforward. As noted, supra, at 506-507, our cases have established that a naturalized citizen’s failure to comply with the statutory prerequisites for naturalization renders his certificate of citizenship revocable as “illegally procured” under 8 U. S. C. § 1451 (a). In 1970, when petitioner filed his application for and was admitted to citizenship, §§ 316 (a) and 318 of the Immigration and Nationality Act of 1952, 8 U. S. C. §§ 1427 (a) and 1429, required an applicant for citizenship to be lawfully admitted to the United States for permanent residence. Lawful admission for permanent residence in turn required that the individual possess a valid unexpired immigrant visa. At the time of petitioner’s initial entry into this country, § 13 (a) of the Immigration and Nationality Act of 1924, ch. 190, 43 Stat. 153, 161 (repealed in 1952), provided that “[n]o immigrant shall be admitted to the United States unless he (1) has an unexpired immigration visa . . . .” The courts at that time consistently held that § 13 (a) required a valid visa and that a visa obtained through a material misrepresentation was not valid. See, e. g., Ablett v. Brownell, 99 U. S. App. D. C. 387, 391, 240 F. 2d 625, 629 (1957); United States ex rel. Jankowski v. Shaughnessy, 186 F. 2d 580, 582 (CA2 1951). Section 10 of the DP A, 62 Stat. 1013, provided that “all immigration laws, . . . shall be applicable to . . . eligible displaced . . . persons who apply to be or who are admitted into the United States pursuant to this Act.” And as previously noted, petitioner was inadmissible into this country under the express terms of the DPA. Accordingly, inasmuch as petitioner failed to satisfy a statutory requirement which Congress has imposed as a prerequisite to the acquisition of citizenship by naturalization, we must agree with the Government that petitioner’s citizenship must be revoked because it was “illegally procured.” See Polites v. United States, 364 U. S. 426, 436-437 (1960); Schwinn v. United States, 311 U. S. 616 (1940); Money v. United States, 278 U. S., at 22-23; United States v. Ginsberg, 243 U. S., at 475; Luria v. United States, 231 U. S. 9, 17 (1913); Johannessen v. United States, 225 U. S. 227, 240 (1912). Cf. Schneiderman v. United States, 320 U. S., at 163 (Douglas, J., concurring). In the lexicon of our cases, one of the “jurisdictional facts upon which the grant [of citizenship] is predicated,” Johannessen v. United States, supra, at 240, was missing at the time petitioner became a citizen.
  B
  This conclusion would lead us to affirm on statutory grounds (and not on the basis of our decision in Chaunt), the judgment of the Court of Appeals. Petitioner argues, however, that in a denaturalization proceeding, a district court has discretion to consider the equities in determining whether citizenship should be revoked. This is the view adopted by the District Court but rejected by the Court of Appeals. It is true, as petitioner notes, that this Cburt has held that a denaturalization action is a suit in equity. Knauer v. United States, 328 U. S. 654, 671 (1946); Luria v. United States, supra, at 27-28. Petitioner further points to numerous cases in which the courts have exercised discretion in determining whether citizenship should be granted. See, e. g., In re Iwanenko’s Petition, 145 F. Supp. 838 (ND Ill. 1956); Petition of R., 56 F. Supp. 969 (Mass. 1944). Petitioner would therefore have us conclude that similar discretion should be available to a denaturalization court to weigh the equities in light of all the circumstances in order to arrive at a solution that is just and fair. He then argues that if such power exists, the facts of this case, particularly his record of good conduct over the past 29 years and the reasonable doubts about some of the allegations in the Government’s complaint, all weigh in favor of permitting him to retain his citizenship. Although petitioner presents this argument with respect to revocation of citizenship procured through willful misrepresentation of material facts, we assume that petitioner believes that courts should also be allowed to weigh the equities in deciding whether to revoke citizenship that was “illegally procured,” which is our holding in this case.
  We agree with the Court, of Appeals that district courts lack equitable discretion to refrain from entering a judgment of denaturalization against a naturalized citizen whose citizenship was procured illegally or by willful misrepresentation of material facts. Petitioner is correct in noting that courts necessarily and properly exercise discretion in characterizing certain facts while determining whether an applicant for citizenship meets some of the requirements for naturalization. But that limited discretion does not include the authority to excuse illegal or fraudulent procurement of citizenship. As the Court of Appeals stated: “Once it has been determined that a person does not qualify for citizenship, . . . the district court has no discretion to ignore the defect and grant citizenship.” 597 F. 2d, at 954. By the same token, once a district court determines that the Government has met its burden of proving that a naturalized citizen obtained his citizenship illegally or by willful misrepresentation, it has no discretion to excuse the conduct. Indeed, contrary to the District Court's suggestion, see supra, at 503, this issue had been settled by prior decisions of this Court. In case after case, we have rejected lower court efforts to moderate or otherwise avoid the statutory mandate of Congress in denaturalization proceedings. For example, in United States v. Ness, 245 U. S. 319 (1917), we ordered the denaturalization of an individual who “possessed the personal qualifications which entitle aliens to admission and to citizenship,” id., at 321, but who had failed to file a certificate of arrival as required by statute. We explained that there was “no power . . . vested in the naturalization court to dispense with” this requirement. Id., at 324. We repeat here what we said in one of these earlier cases:
  “An alien who seeks, political rights as a member of this Nation can rightfully obtain them only upon the terms and conditions specified by Congress. Courts are without authority to sanction changes or modifications; their duty is rigidly to enforce the legislative will in respect of a matter so vital to the public welfare. United States v. Ginsberg, 243 U. S., at 474-475.
  See Maney v. United States, 278 U. S., at 22-23; Johannessen v. United States, 225 U. S., at 241-242.
  In sum, we hold that petitioner’s citizenship must be revoked under 8 U. S. C. § 1451 (a) because it was illegally procured. Accordingly, the judgment of the Court of Appeals is affirmed.
  So ordered.
  The Chief Justice concurs in the judgment.
  Title 8 U. S. C. § 1451 (a) provides in pertinent part:
  “It shall be the duty of the United States attorneys ... to institute proceedings ... in the judicial district in which the naturalized citizen may reside at the time of bringing suit, for the purpose of revoking and setting aside the order admitting such person to citizenship and canceling the certificate of naturalization on the ground that such order and certificate of naturalization were illegally procured or were procured by concealment of a material fact or by willful misrepresentation . . . .”
  Historians estimate that some 800,000 people were murdered at Treblinka. See L. Dawidowicz, The War Against the Jews, 1933-1945, p. 149 (1975); R. Hilberg, The Destruction of the European Jews 572 (1978).
  The District Court described Treblinka in this manner:
  “It contained only living facilities for the SS and the persons working there. The thousands who arrived daily on the trains had no need for barracks or mess halls: they would be dead before nightfall. It was operated with a barbarous methodology — brutally efficient — and such camps surely fill one of the darkest chapters in the annals of human existence, certainly the darkest in that which we call Western civilization.” 455 F. Supp. 893, 901, n. 12 (SD Fla. 1978).
  The DPA incorporated the definition of “refugees or displaced persons” contained in Annex I to the Constitution of the International Refugee Organization of the United Nations (IRO). See §2 (b), 62 Stat. 1009. The IRO Constitution, 62 Stat. 3037-3055, was ratified by the United States on December 16, 1946 (T. I. A. S. No. 1846) and became effective on August 20, 1948. See 62 Stat. 3037.
  The IRO Constitution provided that the following persons would not be eligible for refugee or displaced person status:
  “1. War criminals, quislings and traitors.
  “2. Any other persons who can be shown:
  “(a) to have assisted the enemy in persecuting civil populations of countries, Members of the United Nations; or
  “(b) to have voluntarily assisted the enemy forces since the outbreak of the second world war in their operations against the United Nations.” Annex I, Part II, 62 Stat. 3051-3052.
  The IRO was established in 1946 as a temporary specialized agency of the United Nations to deal with all aspects of the refugee problem in postwar Europe. The IRO established and administered a network of camps and resettlement centers where the refugees were registered, housed, fed, and provided with medical care. Where possible, the IRO provided for the refugees’ rehabilitation and training, arranged legal protection for as long as they were stateless, and negotiated agreements for resettlement. See generally L. Holborn, The International Refugee Organization: A Specialized Agency of The United Nations: Its History and Work 1946-1952 (1956).
  The DPA established a Displaced Persons Commission to oversee and administer the resettlement program envisaged by the Act. 62 Stat. 1012-1013.
  According to testimony presented at trial by one of the Government’s witnesses who served as a vice consul, between 35 and 40 vice consuls were involved in administering the Act. Record 715. Each vice consul spent three months in training in Washington and was then sent to Europe where he received further training before he was put to work reviewing applications. Id., at 711-712, 719-721, 723, 726-727.
  Petitioner also lied about his birthplace and nationality, claiming that he was born in Sarny, in Poland, when in fact he was bom in Sivaseh, in the Ukraine. App. 26. However, on November 21, 1950, after he arrived in this country, petitioner filed an Application for a Certificate of Arrival and Preliminary Form for a Declaration of Intention in which he correctly listed his birthplace as Sivasch in the Ukraine. Petitioner again provided the correct information when he filed a similar form on April 7, 1951. 455 F. Supp., at 911.
  It should be noted that none of the questions in the application for citizenship explicitly required petitioner to disclose this information. Perhaps the most closely related question on the application form was one that required him to list his foreign military service. Petitioner indicated only that he had served in the Russian Army. App. 33.
  See 455 F. Supp., at 896, n. 3.
  The complaint also charged that petitioner had deliberately made false statements for the purpose of securing his naturalization and had thereby failed to satisfy the statutory requirement of good moral character during the 5-year period immediately preceding the filing of his application for naturalization. See 8 U. S. C. § 1427 (a).
  One witness Eugeun Turowski, testified that he saw petitioner shoot and whip Jewish prisoners at the camp. Record 134-136. Another, Schalom Kohn, testified that he saw petitioner almost every day for the first few months Kohn was at Treblinka, id., at 262-263, that petitioner beat him with an iron-tipped whip, and that he saw petitioner whip and shoot other prisoners. Id., at 268, 271, 322-323. The third witness, Josef Czarny, claimed that he saw petitioner beat arriving prisoners, id., at 434, and that he once saw him shoot a prisoner. Id., at 435-442. Gustaw Boraks testified that he saw petitioner repeatedly chase prisoners to the gas chambers, beating them as they went. Id., at 886-888. Boraks also claimed that on one occasion, he heard a shot and ran outside to see petitioner, with a gun drawn, standing close to a wounded woman who later told him that petitioner was responsible for the shooting. Id., at 630-634. Sonia Lewkowicz testified that she saw petitioner shoot a Jewish prisoner. Id., at 973, 1013-1015, 1039-1040. Finally, Pinchas Epstein testified that petitioner shot and killed a friend of his, after making him crawl naked on all fours. Id., at 1056-1070.
  The vice consul’s decision could be overridden by the consul general, but Jenkins testified that he knew of no situation in which this happened. Id., at 721-722.
  On the basis of the vice consuls’ experiences, Jenkins discounted the possibility that any concentration camp guards had served involuntarily. Id., at 756, 772, 795-796. Jenkins reported that all the guards who were questioned by the consular officials about their reasons for serving as guards invariably admitted that their service was voluntary. Id., at 807-808. In addition, Jenkins testified that even if an applicant refused to acknowledge that his service as an armed guard was voluntary, he would still have been denied a visa. Id., at 822-826.
  Jenkins testified that at times concentration camp survivors who recognized a visa applicant as a guard would notify consular officials who in turn investigated the matter. If the accusation proved true, the applicant was confronted with it and invariably found ineligible for a visa. Id.., at 804, 807, 826-827.
  Petitioner testified that there were between 120 and 150 armed Russian guards and some 20 to 30 Germans. Id., at 1444-1445.
  Petitioner testified that between 15 and 20 Russian guards escaped from the camp. Four were caught and apparently executed, but petitioner testified that he did not know what happened to the others. Id., at 1535-1536, 1555.
  The court also noted that there was no dispute about the fact that petitioner lied when he listed his birthplace as Sarny, Poland. 455 F. Supp., at 914.
  The court rejected the witnesses’ pretrial identifications because it found the photo spreads from which the identifications were made imper-missibly suggestive. The court also rejected the in-court identifications by three of the witnesses. The court noted that the first witness initially picked out a spectator in the courtroom and only identified petitioner when it became obvious from the crowd reaction that he had made a mistake. The other two witnesses identified petitioner who was seated at counsel table surrounded by much younger men. The court concluded that the courtroom identifications were tainted by the photo identification and by discussion of the ease among the witnesses.
  The court also found credibility problems with the testimony of the Treblinka survivors, and it concluded that “[e]ven without defendant’s testimony, the Government’s evidence on the claimed commission of atrocities . . . fell short of meeting the ‘clear, convincing and unequivocal’ burden of proof. . . . With defendant’s testimony the Government’s evidence . . . left the court with suspicions about whether defendant participated in atrocities at Treblinka but they were only suspicions.” Id., at 909.
  United States v. Riela, 337 F. 2d 986 (CA3 1964); United States v. Rossi, 299 F. 2d 650 (CA9 1962); La Madrid-Peraza v. Immigration and Naturalization Service, 492 F. 2d 1297 (CA9 1974).
  The court also found that petitioner’s false statements about his birthplace and nationality were not “material” misrepresentations. The court explained that the true facts would not of themselves have justified denial of citizenship since Ukrainians per se were not excluded under the DPA. The court also noted that petitioner disclosed the truth about his place of birth and nationality when he filed Declarations of Intention in 1950 and 1951, and that the INS examiner who interviewed petitioner in connection with his application for citizenship testified that his previous false statements about these questions were not a cause for concern. 455 F. Supp., at 915.
  The Court of Appeals explained that the District Court’s interpretation “destroyed the utility of the second Chaunt test, since it would require, as does the first Chaunt test, that the government prove ultimate facts warranting denial of citizenship.” 597 F. 2d, at 951. The court also pointed out that adopting the District Court’s view would provide a strong incentive to an applicant for a visa or citizenship to lie about his background and thereby prevent an inquiry into his fitness at a time when he has the burden of proving eligibility. If his deception were later uncovered, the Government would face the difficult tasks of conducting an inquiry into his past, discovering facts warranting disqualification, and proving those facts by clear and convincing evidence. Ibid.
  The Court of Appeals noted that its formulation of the second Chaunt test was adopted by the Second Circuit in United States v. Oddo, 314 F. 2d 115, cert. denied, 375 U. S. 833 (1963).
  Because it ruled in favor of the Government under the second Chaunt test, the Court of Appeals had no reason to consider the Government’s claim that, contrary to the District Court’s findings, the evidence at trial clearly and convincingly proved that petitioner committed crimes and atrocities against inmates while he was an armed guard at Treblinka. We accept, for purposes of this case, the District Court’s findings on this issue.
  The Constitution empowers Congress to “establish an uniform Rule of Naturalization.” Art, I, § 8, cl. 4.
  That petitioner gave these false statements because he was motivated by fear of repatriation to the Soviet Union indicates that he understood that disclosing the truth would have affected his chances of being admitted to the United States and confirms that his misrepresentation was willful.
  See Brief for United States 18, n. 13.
  Although the denaturalization statute speaks in terms of “willful misrepresentation” or “concealment of a material fact,” this Court has indicated that the concealment, no less than the misrepresentation, must be willful and that the misrepresentation must also relate to a material fact. See Costello v. United States, 365 U. S. 265, 271-272, n. 3 (1961). Logically, the same principle should govern the interpretation of this provision of the DPA.
  One question on the form Chaunt submitted in connection with his petition for citizenship, asked if he had ever “been arrested or charged with violation of any law of the United States or State or city ordinance or traffic regulation” and if so give full particulars. To this question Chaunt answered “no.”
  Neither the District Court nor the Court of Appeals directly focused on the distinction between false statements in a visa application and false statements in an application for citizenship. The District Court’s opinion suggests that it concluded that there were no willful misrepresentations in petitioner’s 1970 application for citizenship. See 455 F. Supp., at 916-917. The Court of Appeals characterized the case as involving “a misrepresentation by nondisclosure.” 597 F. 2d, at 947.
  Hereafter, references to §§2 (a) and 2 (b), rather than referring to §§ 2 (a) and 2 (b) of the DPA, follow the designation of the definitional provisions in the IRO Constitution, see 62 Stat. 3051-3052, incorporated in § 2 (b) of the DPA.
  Jenkins testified as follows:
  “Q If through investigation or interview you had determined that [a visa] applicant in fact did serve at a death camp ... in occupied Poland as a Ukrainian Guard wopld you have denied the visa application?
  “A Yes, I would.
  “Q And in your expert opinion would such a person have qualified as an eligible displaced person?
  “A No, he would not have.
  “Q I may have asked this question, if I have permit me to ask it again, ... are you aware of any case whatsoever in which an axis auxiliary who served in a capacity as a camp guard was ever legally qualified as a displaced person?
  “A No, I am not. I am reasonably certain that there was no such case.
  “Q Mr. Jenkins, referring to the last question and answer, would it have made any difference whatsoever to you as a visa officer if the person could have been proven to have been a guard but you could not prove that he committed an atrocity?
  “A No.
  “THE COURT: Why? Why?
  “THE WITNESS: Because under the Displaced Persons Act and in the International Refugee Organization constitution by . . . definition such a person could not be a displaced person.” Record 767-768.
  On cross-examination, Jenkins was asked:
  “Q Despite the apparent assumption that a guard at a concentration camp was there voluntarily, a non-German was there voluntarily, if a non-German guard came to you and said to you that his service there was involuntary would that guard have been eligible under the Displaced Persons Act and would he have been granted a visa?
  “A I don’t believe so. In the first place I can’t imagine this hypothetical situation. And secondly, I think the language of the Act is so clear that participation or even acquiesce [nee] in really doesn’t leave the vice consul that kind of latitude.
  “THE COURT: . . . What is there about it that would make you think it was so clear that you had no latitude, if he had according to the hypothetical, persuaded you that his service as a guard was involuntary? How would that differ from involuntary service in the Waffen SS [Axis combat unit] ?
  “A Because the crime against humanity that is involved in the concentration camp puts it into a different category . . . .” Id., at 822-823.
  The District Court felt compelled to impose a voluntariness requirement because it was concerned that a literal interpretation of § 2 (a) would “bar every Jewish prisoner who survived Treblinka because each one of them assisted the SS in the operation of the camp.” 455 F. Supp., at 913. The court noted that working prisoners led arriving prisoners to the lazaret where they were murdered, cut the hair of the women who were to be executed, or played in the orchestra at the gate to the camp as part of the Germans’ ruse to persuade new arrivals that the camp was other than what it was. The court pointed out that such actions could technically be deemed assistance, and concluded that it would be “absurd to deem their conduct ‘assistance or acquiescence’ inasmuch as it was involuntary — even though the word ‘voluntarily’ was omitted from the definition.” Ibid. In addition, the court noted that Jenkins testified that visa applicants who had served in Axis combat units and who could prove that their service was involuntary were found eligible for visas. Id., at 912. But see n. 34, infra.
  The solution to the problem perceived by the District Court, see n. 33, supra, lies, not in “interpreting” the Act to include a voluntariness requirement that the statute itself does not impose, but in focusing on whether particular conduct can be considered assisting in the persecution of civilians. Thus, an individual who did no more than cut the hair of female inmates before they were executed cannot be found to have assisted in the persecution of civilians. On the other hand, there can be no question that a guard who was issued a uniform and armed with a rifle and a pistol, who was paid a stipend and was regularly allowed to leave the concentration camp to visit a nearby village, and who admitted to shooting at escaping inmates on orders from the commandant of the camp, fits within the statutory language about persons who assisted in the persecution of civilians. Other cases may present more difficult line-drawing problems but we need decide only this case. As for the District Court’s concern about the different treatment given to visa applicants who had served in Axis combat units who were found eligible for visas if they could show that they had served involuntarily, this distinction was made by the Act itself.
  The District Court refused to give conclusive weight to Jenkins’ testimony on this issue largely because it felt that Jenkins’ testimony did not recognize the “voluntariness” exception that the court read into § 2 (a). However, Jenkins’ testimony was in accordance with the plain language of the statute. Because the District Court mistakenly applied the law to the facts of this case in concluding that petitioner was lawfully admitted into this country, 455 F. Supp., at 915, we reject its conclusion.
  The dissenting opinion of Justice SteveNS argues that the Government “expressly disavowed” our interpretation of the DPA, post, at 530, and that the Government “unequivocally accepted” the District Court’s construction of § 2 (a), post, at 535. Elsewhere, the dissent suggests that the District Court’s construction is “the Government’s interpretation of the statute,” post, at 536. The sole basis for these assertions is a footnote in the Government’s brief in the Court of Appeals which merely stated: “The United States has no quarrel with [the District Court’s] construction [of §2 (a)] in this case” (emphasis added). In our judgment, none of the dissent’s claims is borne out by this statement. The suggestion that the Government “unequivocally accepted” the District Court’s interpretation of the Act is at best an exaggeration, and we have found no evidence in the record or briefs in this case of the Government’s “express disavowal” of our construction of § 2 (a). Furthermore, being neither endowed with psychic powers nor privy to the Government’s deliberations, we cannot join Justice Stevens, see post, at 535-536, in speculating about the reasons that the Government chose not to “quarrel with” the District Court’s interpretation of § 2 (a) “in this case.”
  As for Justice Stevens’ belief that our interpretation of the statute is “erroneous,” see post, at 533, we simply note that he is unable to point to anything in the language of the Act that justifies reading into § 2 (a) the “voluntariness” limitation that Congress omitted. Thus, we must conclude that Justice Stevens’ real quarrel is with Congress, which drafted the statute. It is not the function of the courts to amend statutes under the guise of “statutory interpretation.” See Potomac Electric Power Co. v. Director, Office of Workers’ Compensation Programs, ante, at 274. Finally, since the term “persecution” does not apply to some of the tasks performed by concentration camp inmates, see n. 34, supra, we reject the speculation that our decision “may jeopardize the citizenship of countless survivors of Nazi concentration camps,” post, at 530 (Stevens, J., dissenting).
  Title 8 U. S. C. § 1429 provides in pertinent part: “[N]o person shall be naturalized unless he has been lawfully admitted to the United States for permanent residence in accordance with all applicable provisions of this chapter.” See also 8 U. S. C. § 1427 (a).
  The same requirement is now contained in 8 U. S. C. § 1181 (a) which provides that “no immigrant shall be admitted into the United States unless at the time of application for admission he (1) has a valid unexpired immigrant visa
  See H. R. Rep. No. 1086, 87th Cong., 1st Sess., 39 (1961) (Citizenship is illegally procured if “some statutory requirement which is a condition precedent to naturalization is absent at the time the petition [for naturalization is] granted”).
  Courts must consider the facts and circumstances in deciding whether an applicant satisfies such requirements for naturalization as good moral character and an understanding of the English language, American history, and civics. See 8 U. S. C. §§ 1423, 1427 (d).
  Our decision makes it unnecessary to resolve the question whether the Court of Appeals correctly interpreted the materiality test enunciated in Chaunt.