In the 1966 case Berenyi v. District Director, Immigration and Naturalization Service, the U.S. Supreme Court ruled in favor of Peter Berenyi, a Hungarian refugee seeking naturalization as an American citizen. The court held that doubts concerning eligibility for citizenship must be resolved in favor of the applicant unless there is "clear, unequivocal and convincing" evidence to suggest otherwise. The case arose when Mr. Berenyi was denied citizenship on grounds that he had given false testimony about his membership in a communist organization while living in Hungary before fleeing to America during the 1956 revolution against Soviet control. However, it was found that this denial was based on insufficient evidence; thus violating due process rights under Fifth Amendment protections.

In the dissenting opinion for Berenyi v. District Director, Immigration and Naturalization Service, Justice Harlan argued that the majority's decision was based on an incorrect interpretation of the naturalization laws. He contended that these laws do not require absolute certainty about every detail in a petitioner's past but rather "a reasonable belief" based on credible evidence. In this case, he believed there was sufficient evidence to support Mr. Berenyi’s claim of good moral character despite his failure to disclose certain details about his wartime activities during World War II when applying for citizenship. Furthermore, Justice Harlan criticized the majority's view as unrealistic and impractical because it would place an impossible burden on immigration officials who are tasked with making decisions about naturalization applications.