'Workers Insurance's Massacre') occurred on 5 September 1938, and was the Chilean government's response to an attempted coup d'état by the National Socialist Movement of Chile (MNSCh), whose members were known at the time as Nacistas ("Nazis").

[3] Initially receiving funds and members from Germans living in Chile and reaching a membership of over 20,000, The movement stressed need for one-party rule, corporatism and solidarity between classes, and soon set up its own paramilitary wing, the Tropas Nacistas de Asalto.

[6][7] The failure of the coup ultimately led to Ibanez removing himself from the race, and the Popular Front candidate Pedro Aguirra Cerda winning by a narrow margin.

José Luis Salazar, a carabinero (uniformed police) who was on watch, upon observing the situation, thought that the Nacistas were concealing weapons under their coats, and prepared to respond.

This culminated in a shoot-out as well, beginning at 02:00, when an assault by the carabineros took members of the National Socialist group by surprise; those who surrendered were led with their hands up, toward the Seguro Obrero a few blocks away.

[12] Although the accusations are grounded in speculation, it is argued by Marcus Klein in La Matanza del Seguro Obrero, and accepted by many historians that Alessandri gave the execution order.