Watkins v. United States, Supreme Court of the United States, No. 261, October Term-1956, slip opinion, June 17, 1957
The Supreme Court heard the case of Watkins v. United States, which challenged Congress’s expansive investigative power, in October 1956 and published its decision in June 1957. The court cited an 1881 legal precedent, Kilbourn v. Thompson, in upholding the Bill of Rights over Congress’s right to demand information not strictly relevant to an investigation.
Manuscript Division, Library of Congress

Constitutional Rights v. Congressional Powers
From the 1930s through the 1950s, Congress intensively investigated perceived political radicals. The House Committee on Un-American Activities focused on suspected communists in the film industry, universities, and labor organizations. Some witnesses refused to testify, pleading the Fifth Amendment—the right not to incriminate oneself. In 1954 labor organizer John Thomas Watkins directly challenged a subcommittee’s right to demand information not pertinent to the investigation. Watkins was convicted of contempt of Congress, but in 1957 the United States Supreme Court decided in his favor, limiting Congress’s investigative powers.
The Bill of Rights is applicable to congressional investigations, as it is to all forms of governmental action
Chief Justice Earl Warren, Watkins v. United States, 1957