In the case of Tenney et al. v. Brandhove, 1950, the U.S Supreme Court ruled in favor of California State Senator Jack B. Tenney and other members of a legislative committee who were sued by William Brandhove for alleged conspiracy to deter him from exercising his First Amendment rights through intimidation and false accusations during an investigation into communist activities in California. The court held that legislators are immune from liability for their legislative acts under Section 1983 (Civil Rights Act) which provides redress for deprivation of civil rights under color of state law, even if their conduct was malicious or they had improper motives. This ruling is based on the Speech or Debate Clause found in Article I, Section 6 of the Constitution which grants immunity to lawmakers "for any speech or debate" made within their official capacities as legislators.

In the dissenting opinion for Tenney et al. v. Brandhove, Justice William O. Douglas argued that legislative immunity should not be absolute and unqualified in all circumstances. He contended that when a committee of legislators acts outside its jurisdiction or abuses its powers to infringe upon an individual's constitutional rights, it should be held accountable for such actions in court. In this case, he believed that Brandhove had been denied his First Amendment rights by being subjected to harassment and intimidation through repeated subpoenas from the California Senate Fact-Finding Committee on Un-American Activities - a committee which he claimed was acting beyond its legitimate scope of inquiry into state affairs by investigating federal matters instead. Therefore, contrary to the majority opinion which upheld legislative immunity as an essential part of separation of powers doctrine under the U.S Constitution, Justice Douglas advocated for judicial review as a necessary check against potential misuse or overreach of power by legislators.