Clashes began when units of the Guardia Civil under the influence of the Stalinist Communist Party of Spain and its local wing, the Unified Socialist Party of Catalonia (PSUC) attempted to take over an anarchist-run telephone building in Barcelona. The telephone workers fought back, sparking a city-wide conflict. Five days of street fighting ensued, with anarchist workers and their allies (Friends of Durruti Group), supporters of the non-Stalinist Workers' Party of Marxist Unification (POUM), building barricades and exchanging fire with the Assault Guards, stormtroopers and PSUC.
Confederación Nacional del Trabajo (CNT) workers were eventually persuaded into a compromise by Juan García Oliver, amongst others. The Republican government sent 10,000 Assault Guard troops to Barcelona to quell the fighting. The ultimate result of the battle was the further erosion of worker control of the city and the consolidation of government power over the major labor organizations in Catalonia, the CNT and its sister group, the Federación Anarquista Ibérica (known collectively as the CNT-FAI).
The British author George Orwell describes these events, which he witnessed and took part in, in his famous book Homage to Catalonia. The Swedish socialists Ture Nerman and August Spångberg were also present in Barcelona, and they both write about their experiences in their autobiographies.
Ibárruri ascribes to the events to an "anarchotrotskyist" attempt at shutting down the Republican government on orders from General Francisco Franco, acting in tandem with Adolf Hitler. According to her, the violence was the culmination of an anarchist plot which included plans to stop the movement of trains and cut all telegraph and telephone lines; she cites an "order [from the Catalan government] to its forces to control the telephone building and disarm all people whom they encounter in the streets without proper authorization" as the aim of the anarchist plan. She does not provide any evidence to support these claims, which were widely held by fellow Party members at the time but have since been discredited.
The Communist party alleged the anarchist "putsch" to be motivated by their resentment of the centralized military command sought by the Communists and their allies the Catalan government under Lluis Companys, and desire to seize political power.