In the United States v. Moser case of 1924, the Supreme Court ruled on a matter involving federal employment and racial discrimination. The defendant, Philip J. Moser, was an official in charge of hiring at a U.S naval shipyard who had been convicted for refusing to hire African-American workers based solely on their race. On appeal, his primary argument was that he could not be prosecuted under criminal law because there were no specific laws against racial discrimination in government hiring practices at that time. The Supreme Court disagreed with this argument and upheld Moser's conviction by affirming two key principles: First, all citizens have equal rights to federally funded job opportunities; secondly, any public officer who denies these rights due to prejudice can be held criminally liable under existing statutes prohibiting fraud or misappropriation of funds. This decision marked one of the earliest instances where the court explicitly recognized anti-discrimination as a principle within American law.

In the dissenting opinion for United States v. Moser, Justice McReynolds disagreed with the majority's decision to uphold a conviction based on an act that was not illegal at the time it was committed. He argued that this violated basic principles of justice and fairness, as individuals should only be held accountable for their actions if they were aware or could reasonably have been expected to know that what they were doing was against the law. Furthermore, he contended that retroactively applying laws in this manner undermines public confidence in legal institutions by creating uncertainty about what is and isn't permissible behavior. This unpredictability can deter people from engaging in activities which are perfectly lawful out of fear of potential future prosecution.