In the United States v. Gillock case of 1979, the U.S. Supreme Court ruled that a state legislator did not have immunity from federal prosecution for bribery-related charges under the Speech or Debate Clause in Article I of the Constitution. The court held that while members of Congress were protected by this clause, it did not extend to state legislators like William L. Gillock, who was a member of Tennessee's General Assembly and had been indicted on several counts related to accepting bribes for influencing legislation. The court argued that extending such protections could interfere with federal law enforcement efforts and undermine public trust in government institutions.

In the dissenting opinion for United States v. Gillock, Justice Brennan argued that the majority's decision to allow a federal court to pierce a state legislator's immunity was incorrect. He believed that this ruling undermined the principles of federalism and separation of powers by allowing federal courts to interfere with state legislative processes. Furthermore, he contended that there were other ways in which corruption could be addressed without infringing upon these constitutional protections, such as through state prosecutions or disciplinary actions within the legislature itself. In his view, it was not necessary or appropriate for federal courts to intrude into matters traditionally reserved for states' self-governance.