The House Un-American Activities Committee (HUAC) was a committee of the U.S. House of Representatives, investigated allegations of communist activity in the U.S. during the early years of the Cold War (1945-91). Established in 1938, the committee wielded its subpoena power as a weapon and called citizens to testify in high-profile hearings before Congress. This intimidating atmosphere often produced dramatic but questionable revelations about Communists infiltrating American institutions and subversive actions by well-known citizens. HUAC’s controversial tactics contributed to the fear, distrust and repression that existed during the anticommunist hysteria of the 1950s. By the late 1950s and early 1960s, HUAC’s influence was in decline, and in 1969 it was renamed the Committee on Internal Security. Although it ceased issuing subpoenas that year, its operations continued until 1975.
The consequences of refusing to answer questions would be the indefinite "blacklisting" of that particular person. Blacklisting meant they were considered a Communist and their career would be destroyed forever. Many Hollywood actors and political figures during this time were accused of being a Communist and had to stand trial. In fact, a number of them have never been able to recover from the accusations.