In the case of United States ex rel. Eichenlaub v. Shaughnessy, 1949, the U.S Supreme Court ruled on whether a naturalized citizen could be denaturalized and deported based on pre-naturalization activities that were not disclosed during their naturalization process. The appellants, Frederick William Eichenlaub and Elsa Ida Spitz Eichenlaub, both German-born American citizens who had been convicted of espionage for Germany during World War II before they became citizens in 1943. They were ordered to be deported under an immigration law which allowed deportation if it was found that citizenship was obtained through fraud or misrepresentation. The court held that while there is no statute allowing for denaturalization due to fraudulent procurement of citizenship specifically because of pre-citizenship illegal activity undisclosed at the time of naturalization proceedings; however, such actions can still lead to deportation under existing immigration laws if these acts are deemed contrary to good moral character required for citizenship application approval. This ruling affirmed the power and discretion given by Congress to administrative agencies like Immigration Services in determining what constitutes 'good moral character' as well as their ability to deport individuals whose behavior contradicts this standard even after they have gained citizenship.

In the dissenting opinion for United States ex rel. Eichenlaub v. Shaughnessy, Justice Jackson argued that the majority's decision to deport two naturalized citizens who had been convicted of espionage was a misinterpretation of immigration law and an overreach of executive power. He contended that under U.S. law, only non-citizens could be deported and citizenship could not be revoked without due process in court proceedings separate from criminal trials for unrelated offenses such as espionage. Furthermore, he asserted that allowing deportation based on convictions obtained before naturalization would set a dangerous precedent by retroactively punishing individuals for past crimes after they have already served their sentences - effectively imposing double jeopardy in violation of constitutional rights.