Kilbourn v. Thompson

However, the Court was not willing to go so far as to say that the members of Congress who had improperly conducted their investigation should be punished. The Constitution holds that members of Congress "shall not be questioned in any other place" for any speech or debate that takes place in Congress. The framers of the Constitution believed such a provision was necessary if members of Congress were to feel free to make laws that might sometimes be unpopular or controversial. Therefore, no one who had been elected to Congress could be punished for what happened to Kilbourn.

Thompson, however, was not a member of Congress, and he could be punished. The question of what his punishment should be was remanded to a lower court. Meanwhile, however, the Supreme Court had established an important principle: Congress had no right to investigate the affairs of a private citizen, nor to punish private citizens for refusing to answer questions in improper investigations. Although later Court decisions gave Congress somewhat more latitude to investigate and interrogate, Kilbourn v. Thompson was an important step in defining the scope of congressional powers.