The Communist League of Struggle (CLS) was a factional offshoot of the Communist League of America (Opposition), the Left Opposition group headed by James P. Cannon. The organization was formed on March 15, 1931, owing to what it claimed was "the utter incapacity of the other groups, with their false policies and practices, to lead the workers successfully toward the proletarian revolution."

The leading forces in the CLS were textile union activist Albert Weisbord, a 1924 graduate of Harvard Law School and member of the Workers (Communist) Party of America from that same year, and his wife Vera Buch, an activist in the Left Wing Section of the Socialist Party of America from 1919 and member of the Communist Party of America from 1920.

The Communist League of Struggle (CLS) did not publish a tally of its membership. Given the fact that the Communist League of America (Opposition), the group from which it split, had a membership of "less than 200" during the 1931-1933 period, it seems highly probable that the CLS began with a membership of fewer than 50.

The CLS pointedly styled itself a "vanguard party" which adhered to "the International Left Opposition, led by Leon Trotsky." The group was sympathetic to the concept of the United Front and for the formation of a "mass labor party on a federated basis that will move the working clas of this country to independent political action."

The CLS took a harsh rhetorical stance towards the other three Communist organizations that existed at the time of its formation -- the Communist Party USA, the Communist League of America (Opposition), and Jay Lovestone's Communist Party (Majority Group) -- stating that "it considers the other three groups as 'right-wing' opportunist groups, each differing in form and manner, but each overestimating the enemy and underestimating the proletariat."

[fn. Nathan Fine (ed.), The American Labor Year Book, 1932. (NY: Rand School Press, 1932), pp. 119-123.]