While Margo continued to act in films until the 1960s, her career was curtailed by the television blacklist that began in 1950, with the targeting of Gypsy Rose Lee, Jean Muir, Hazel Scott, and Ireene Wicker. Margo was known for her progressive political views, but she was not a member of the Communist Party. In 1950, her name and that of her husband were published in "Red Channels", an anti-Communist pamphlet that purported to expose Communist influence within the entertainment industry. "Red Channels" labeled her a communist because of her support for the Hollywood Ten, her advocacy for peace, and her support for refugees.