In its XXV Congress that took place from 31 July to 5 August 1971, the Radical Party confirmed the left-wing line it had taken already in 1967.

Disquieted by the Marxist influence,[3] on 3 August, the Senators Bossay, Baltra, Acuña, Juliet and Aguirre and deputies Ibáñez, Magalhaes, Naudón, Basso, Clavel, Sharpe and Muñoz Barra left the Radical Party.

The radical minister of justice Manuel Sanhueza held talks with the Christian Democratic Party over regulations of nationalized firms, but ultimately failed, as the socialist minister of economy Pedro Vuskovic boycotted the negotiations and carried out legally dubious expropriations.

One faction called for a Yes vote on the referendum (for Pinochet), and formed a new ephemeral Chilean Social Democrat Party that soon merged with the Progressive Union of the Centrist Centre.

The other faction called for a No vote and joined the opposition cartel Concertación de Partidos por la Democracia, and eventually merged with the Radical Party to form the Social Democrat Radical Party.