In the United States v. Brown case of 1964, the Supreme Court ruled on whether a member of the Communist Party could serve as an executive officer in a labor union. Robert G. Brown had been indicted under Section 504 of the Labor-Management Reporting and Disclosure Act for serving as Secretary-Treasurer of his local longshoremen's union while being a known member of the Communist Party. The District Court dismissed this indictment, but it was reinstated by an Appeals court. The Supreme Court held that Section 504 violated First Amendment rights to freedom of speech and association, along with Fifth Amendment protections against self-incrimination and deprivation without due process. It found that Congress had overstepped its bounds by making membership in certain political parties illegal rather than focusing on specific actions or behaviors which might be harmful to national security or labor relations. This decision emphasized that laws cannot punish individuals simply based on their affiliations or beliefs; they must instead focus on concrete actions taken by those individuals which are detrimental to society at large.

In the dissenting opinion for United States v. Brown, Justice Hugo Black argued that the Smith Act, which made it a crime to be a member of an organization advocating violent overthrow of the government, was unconstitutional as applied in this case. He contended that mere membership in such an organization did not necessarily mean active participation or agreement with its unlawful objectives. Furthermore, he believed that criminalizing membership violated First Amendment rights to freedom of speech and association. Justice Black also criticized the majority's reliance on "guilt by association" principles and their failure to require proof beyond reasonable doubt regarding Brown's specific intent to further illegal activities through his Communist Party affiliation.