The international volunteers were mainly socialists, communists, or others willing to accept communist authority, and a high proportion were Jewish. Some were involved in the Barcelona May Days fighting against leftist opponents of the Communists: the Workers' Party of Marxist Unification (POUM) ("Partido Obrero de Unificación Marxista", an anti-Stalinist Marxist party) and the anarchist CNT (CNT, Confederación Nacional del Trabajo) and FAI (FAI, Iberian Anarchist Federation), who had strong support in Catalonia. These libertarian groups attracted fewer foreign volunteers.