The Workers' Party of Marxist Unification (POUM) was a Spanish communist political party that existed from 1935 to 1980. The POUM was opposed to the Stalinist government of the Soviet Union, and it followed the ideas of Leon Trotsky. The party grew larger than the Communist Party of Spain (PCE) both nationally and in the communist hotbeds of Catalonia and the Valencian Community, and its membership grew from 10,000 in July 1936 to 70,000 in December 1936. The Communist Party accused POUM of Trotskyism and even fascism, leading to rifts between the two parties that led to the May Days of June 1937, in which PCE militiamen rounded up anarchists and Trotskyists across Catalonia and executed them; co-founder Andreu Nin was executed by the Stalinists. By June 1937, POUM membership had dropped to 40,000. In 1977, after years of being exiled in London, the POUM was legalized in Spain, and it merged into the Left Bloc for National Liberation in 1980.