 He was an adherent of the Militant faction of the Socialist Party and was chairman of its Revolutionary Policy Committee and sat on the board of directors of the League for Industrial Democracy.Matthews' association with the Socialist Party and its auxiliaries proved to be short-lived, however.In 1933, he was a speaker at a rally at Madison Square Garden sponsored by the United States Communist Party as part of its united front campaign, action which led to a reprimand and eventually to the suspension of Matthews for "conduct unbecoming a member" of the Socialist Party.