In 1923, by now using the Americanized name "Steve Nelson," he joined the youth section of the American Communist Party, the Young Workers League. He went on to join the adult Workers (Communist) Party in 1925. That year, he moved (with his new wife) to Detroit, where he worked in the auto industry as an assembly line worker and union organizer. In 1928, they moved to New York City, where Nelson studied Marxism at the New York Workers School. With the onset of the Great Depression, husband and wife worked for the Communist Party full-time.