In Viereck v. United States (1942), the U.S. Supreme Court upheld a conviction under the Foreign Agents Registration Act of 1938, which required agents representing foreign principals in political or quasi-political activities to disclose their relationship and information about related finances and activities. The appellant, George Sylvester Viereck, was convicted for failing to register as an agent of Germany during World War II while disseminating propaganda on its behalf. He argued that this violated his First Amendment rights and claimed that he was not given fair warning by the law's language regarding what constituted "political activity". However, the court rejected these arguments stating that terms used were sufficiently clear in context and did not violate constitutional requirements for definiteness.

In the dissenting opinion for Viereck v. United States, Justice Murphy argued that the conviction of Viereck under the Foreign Agents Registration Act should be overturned due to a lack of evidence proving his guilt beyond reasonable doubt. He contended that while there was substantial evidence showing Viereck had failed to disclose certain activities in his registration statement, it wasn't clear whether these omissions were intentional or merely oversights. Furthermore, he pointed out that some of the information omitted from Viereck's statement did not seem relevant to national security and therefore may not have been necessary for him to include in order to comply with the law. Thus, Justice Murphy believed that convicting someone based on such ambiguous circumstances set a dangerous precedent and undermined principles of justice.