Later: Thanks, good work all.
From the same source: "He had decided to give in to the committees' demands and appeared before it again in 1951 and acknowledged that he had briefly belonged to the party between 1944 and 1945. ... His testimony required him to name others who had also been involved with the Communist Party, and gave the committee the name of six directors."
From what I read in the text, they refused to verify or deny their relations to the Communist Party. --Yooden
They were cited by the full House of Representatives for contempt of Congress (as recommended by the committee), indicted by a federal grand jury, tried and convicted in a federal district court, and their convictions were upheld by the federal appeals courts, including the Supreme Court, which declined to review the case.
They were "blacklisted" by the Hollywood studio heads, who declared that they would be suspended or fired and not rehired until they were acquitted or purged of contempt and had sworn they were not Communists.
Their appearance before the committee was in October 1947, the blacklisting in November. The trials were in the spring of 1948, and they went to jail in 1950.
Tthe contempt charges arose from their efforts to disrupt the committee's proceedings while refusing to answer questions put to them by the committee concerning their Communist affiliations and activities. The committee was investigating Communist influence in the Hollywood labor unions. Among the questions they refused to answer was, "Are you a member of the Screen Writers Guild?" - HWR
Good research, so go put it on the Hollywood Ten page