 During the 1930s and 1940s, Parker became an increasingly vocal advocate of causes like civil liberties and civil rights, and a frequent critic of those in authority. She reported on the Loyalist cause in Spain for the Communist magazine The New Masses in 1937. At the behest of Otto Katz, a covert Soviet Comintern agent and operative of German Communist Party agent Willi Muenzenberg, Parker helped to found the Hollywood Anti-Nazi League in 1936 (which was suspected by the FBI of being a Communist Party front). The Hollywood Anti-Nazi League's membership eventually grew to some 4,000 strong. Its often wealthy members' contributions (probably not intended to support Communism) were, in the words of David Caute, "able to contribute as much to [Communist] Party funds as the whole American working class".
