The Marxist Workers League was the name of two splinter groups from the Revolutionary Workers League in the 1930s.
The first group split in early 1936 and "after a sensational existence of both its members for 19 days" rejoined the Trotskyists.
The second group formed in early 1938, containing elements both from the RWL and from Albert Weisbords Communist League of Struggle, as well as some Trotskyists from the YPSL. Its central criticism of the RWL was of its analysis of the Spanish Civil War, which it believed was an imperialist war. Its principal leader was K. Mienev.
The MWL published a "theoretical organ" out of New York called Spark, and then Power from February 1938 to 1940. According to Walter Goldberg, Spark lasted from Vol. I #1 Feb. 1938 to Vol. II #3 May 1939. About that time the group merged with another small sect, the Revolutionary Marxist League, led by Attilio Salamme and Karl Joerger, to create a group called the Workers Party. This new sect appears to have died out quickly, and should not be confused with the Shachtmanite Workers Party that was formed around the same time.