The Communist Party USA was established in 1919. In 1921 it changed its name to The Workers Party of America. It was banned in 1954 by an act of Congress (the Communist Control Act of 1954). At its peak in 1944 the membership rose to 80.000 members but by mid-1950s it dropped to only 5000 members, including 1500 FBI informants.
Matt Cvetic really was a Pittsburgh native who really was asked by the Federal Bureau of Investigation to join the Communist Party of the USA as an informant in the 1940s. By 1948 he was earning $85 per week from the FBI for his work, although he continually pressured the Bureau to increase his salary to $100 and threatened to quit if his requests were not granted (they weren't, and he didn't). He told what he was the true story of his experience in a series of articles in the Saturday Evening Post. His experiences were first dramatized in a radio program, which was later adapted for a Warner Brothers motion picture in 1951. He also testified before the House Un-American Activities Committee in the 1950s. Although the radio and film adaptations portrayed Cvetic as one of the party's primary operatives in the USA, he didn't actually rise above the party's lower echelons. By 1955, Cvetic had been largely discredited as a witness regarding communist activities in the USA because of Justice Department and FBI concerns regarding Cvetic's embellishment of the facts, including an instance in which he claimed to have defused a Nazi spy plot single-handedly.