Also on the American Waterfront people appealed for labor actions to refuse to load arms for Franco or not to sail on any ships carrying cargo consigned to the fascists.
Two pamphlets written by Roy Hudson are worth reading:
Additional information can be found in:
Nelson, Bruce: Workers on the Waterfront: Seamen, Longshoremen, and Unionism in the 1930s (Working Class in American History), 1990
Smith, Eric R.: American Relief Aid and the Spanish Civil War, 2013