In the 1906 case of Romeu v. Todd, the U.S. Supreme Court was asked to consider whether a Cuban citizen who had become a naturalized American citizen could be denied entry into Cuba based on his new citizenship status. The plaintiff, Jose Ignacio Romeu, argued that he should not be barred from returning to his homeland simply because he had chosen to become an American citizen. However, the court ruled against him and upheld the decision of lower courts which stated that once someone becomes a naturalized U.S. citizen they lose their previous nationality and any rights associated with it in foreign countries unless there is an existing treaty between those two nations allowing for dual citizenship or similar arrangements.

In the dissenting opinion for Romeu v. Todd, Justice Harlan argued that the majority's decision was a misinterpretation of both international and domestic law. He contended that under international law, an individual does not lose their original nationality until they have completed all necessary steps to gain new citizenship in another country. In this case, he believed Mr. Romeu had not fully renounced his American citizenship as he had only declared his intention to become a citizen of Spain but did not complete the process before returning to America. Furthermore, Justice Harlan disagreed with the majority's interpretation of U.S immigration laws which allowed for deportation based on criminal convictions abroad; arguing it should apply only if such conviction occurred after gaining U.S citizenship rather than prior to it as in Mr.Romeu’s case.