The Communist League of America (CLA) was founded in 1929 by James P. Cannon, Max Schachtman, and Martin Abern following their expulsion in 1928 from the Workers (Communist) Party. In 1934 the CLA merged with the American Workers Party to form the Workers Party of the United States. Collection contains correspondence, memoranda, internal party bulletins, financial reports and other documents relating to the activities of the Communist League of America.

Collection contains letters, memoranda, internal party bulletins, financial reports, and other documents relating to the activities of the Communist League of America (Opposition) and the publication of its newspaper, The Militant. Includes correspondence between James P. Cannon and Martin Abern and other party organizers including S. Gendelman in New Haven, Connecticut.