In Eastland v. United States Servicemen's Fund, the Supreme Court ruled in favor of Senator James O. Eastland and other members of a Senate subcommittee who were investigating whether certain organizations, including the U.S. Servicemen's Fund (USSF), posed threats to military morale and discipline. The USSF had filed suit against the committee for subpoenaing its bank records without providing an opportunity for judicial review, claiming this violated their First Amendment rights by inhibiting freedom of speech and association as well as Fourth Amendment rights against unreasonable searches and seizures. The court held that legislative immunity protected congressional investigations from judicial interference if they fell within Congress’s legitimate legislative sphere; it found that such was indeed the case here because oversight over military affairs is clearly part of Congress’s constitutional responsibilities. Therefore, even though subpoenas might have some chilling effect on free expression or could be seen as invasions of privacy under different circumstances, these concerns did not outweigh Congress’ need to gather information relevant to potential legislation in this instance.

In the dissenting opinion for Eastland et al. v. United States Servicemen's Fund et al., Justice Douglas argued that the majority had erred in its interpretation of the Speech or Debate Clause, which he believed was not intended to protect all activities related to legislative duties but only those integral to deliberation and decision-making processes. He contended that a subpoena issued by a Senate subcommittee seeking bank records of an organization critical of U.S military policy violated First Amendment rights as it constituted governmental interference with freedom of speech and association without sufficient justification. In his view, such actions were beyond congressional authority unless directly tied to legitimate legislative purposes - something he did not believe was demonstrated in this case.