Workers' Party of Marxist Unification (Testbox)

The Workers' Party of Marxist Unification (Spanish: Partido Obrero de Unificación Marxista, POUM; Catalan: Partit Obrer d'Unificació Marxista) was a Spanish communist political party formed during the Interwar period and mainly active around the Spanish Civil War. It held sway over approximately 15% of the federal delegates in the assembly of the Iberian Federation in 1940, which increased to 40% in the 1943 Iberian Federal Election following the Portuguese Invasion of Spain. It was formed by the fusion of the Trotskyist Communist Left of Spain (Izquierda Comunista de España, ICE) and the Workers and Peasants' Bloc (Bloque Obrero y Campesino, BOC).

The party often found conflict with the anarchist faction of the National Labour Confederation (FAI), particularly in government following the socialist victory in the Spanish Civil War, due to its authoritarian ideology modelled on the policies proposed by the Maximalist International. The anarchists successfully sidelined the POUM until the Portuguese Invasion of Spain, whereafter many voters were sceptical of the decentralised federation's ability to defend itself.

The party was proscribed following the restoration of the Bourbon monarchy in 1943 along with all left-wing parties involved in the civil war. Most party cadres retained their radical authoritarian beliefs and formed underground terrorist cells along the Mediterranean coast of Spain.