If a witness stated that he was a Communist, he was then required by Parnell Thomas to inform on his fellow party members. If he declined to do so, he went to jail for contempt. If he denied that he was a Communist and was then proved to be a party member, he went to jail for perjury, and if he refused to answer the question at all, he could go to jail for contempt of Congress.

In the end ten witnesses went to jail, the best known of whom were the writer John Howard Lawson, whom Parnell Thomas ordered to be forcibly removed from the witness stand by armed guards when he insisted loudly that his rights as an American citizen were being invaded; Dalton Trumbo, the writer, who was refused an opportunity to cross-question witnesses when they stated that he had Communist Party affiliations; the writer Sam Ornitz, who was also forcibly removed after an altercation with Parnell Thomas; the well-known director Eddie Dmytiyk, who, because he claimed constitutional immunity, was refused a chance to cross-question witnesses; and the writer Ring Lardner, Jr., who was denied the opportunity to read a closing statement in his own defence.