After the congress of Christian Associations of Italian Workers (ACLI) had voted the end of collateralism with the Christian Democracy, on March 8th 1969 Livio Labor (that was president of ACLI) founded with Riccardo Lombardi the "Association of Political Culture" (Associazione di Cultura Politica, ACPOL), committed to the restructuring of the Italian left. On 5 July 1970, the ACPOL broke up to start the constituent phase of the Workers' Political Movement (MPL). The MPL had the objective of representing the Catholic area of dissent towards the DC and in this sense it should have catalyzed the consensus of progressive Catholics and leftists.
In the general elections of 1972 the MPL obtained only 0.36% of the votes. After this disappointing result many MPL members (like the same Labor, Gennaro Acquaviva, Luciano Benadusi, Marco Biagi and Luigi Covatta) joined the Italian Socialist Party.
The MPL minority (Giovanni Russo Spena, Domenico Jervolino, Gian Giacomo Migone, Vittorio Bellavite and others) decided instead to continue its political activity as Socialist Alternative. Three months later this new formation merged with the New Italian Socialist Party of Proletarian Unity to found the Proletarian Unity Party (PdUP).