In Savorgnan v. United States, the Supreme Court ruled in 1949 that an American citizen who voluntarily and knowingly obtained citizenship of a foreign country lost their U.S. citizenship, even if they did not intend to relinquish it. The case involved Mrs. Savorgnan, a naturalized U.S citizen who became an Italian citizen through her marriage to an Italian man while residing in Italy during World War II - as required by Italian law at the time. Upon returning to the US after the war ended, she was deemed by State Department officials as having renounced her American citizenship when she acquired Italian nationality and denied entry into America on this basis. The court held that under Section 401 (g) of Nationality Act of 1940 which states "a person shall lose his nationality by...voting in political election or plebiscite taking place in foreign state", Mrs Savorgnan had effectively expatriated herself from America upon obtaining Italian Citizenship regardless of whether she intended to retain her US Citizenship or not. This decision underscored how actions taken abroad could impact one's status as a U.S citizen under existing immigration laws at that time.

In the dissenting opinion for Savorgnan v. United States, Justice Jackson argued that the majority's decision was a dangerous precedent to set. He believed it allowed Congress too much power in determining who could and couldn't be considered an American citizen, which he saw as a violation of individual rights. He also disagreed with the idea that someone could lose their citizenship simply by becoming a citizen of another country without explicitly renouncing their U.S. citizenship first. Furthermore, he pointed out inconsistencies in how this rule had been applied historically and warned against using such arbitrary criteria to determine something as important as nationality status.