It remained small throughout its existence and in 1968 it shrunk further when a sector of its militants abandoned the party to join the Organisation of Marxist–Leninists of Spain.

[4] In January 1971, at the time when the need was felt to renew the fight against the Francoist rule of Spain, the then Communist Party of Spain (Marxist–Leninist), together with the Spanish National Liberation Front (FELN) and Vanguardia Socialista, took part in the foundation of the Revolutionary and Patriotic Antifascist Front (FRAP)[5] at a meeting in Paris held in a house owned by American writer Arthur Miller.

Initially the Front was led by Julio Álvarez del Vayo, FELN leader and a former member of the Spanish Socialist Workers' Party.

In 1977, during the Spanish transition to democracy, it started publishing Vanguardia obrera as the organ of the Central Committee of the party.

[3] That year, a split surged in the party, with a dissident group forming a parallel PCE(m-l) and publishing its own version of Vanguardia obrera.