In Eastland v. United States Servicemen's Fund the United States Supreme Court held that even in the face of an alleged infringement of first amendment rights, when a Senate subcommittee's activity falls within the "legitimate legislative sphere," the speech or debate clause of the United States Constitution protects the activities of the subcommittee, the individual senators and the chief counsel, thereby prohibiting judicial interference to enjoin a subpoena issued by the subcommittee.
Copelan, John J. Jr.
"Constitutional Law--Legislative Immunity Outweighs First Amendment Rights,"
Mercer Law Review: Vol. 27:
4, Article 15.
Available at: https://digitalcommons.law.mercer.edu/jour_mlr/vol27/iss4/15