|Founded||October 1, 1922|
|Banned||1 November 1925|
|Split from||Italian Socialist Party|
|Merged into||Italian Socialist Party|
|Political position||Centre-left to left-wing|
|International affiliation||Labour and Socialist International|
The party was founded in November 1922 by the reformist wing of the Italian Socialist Party (PSI) led by Filippo Turati and Giacomo Matteotti, after they had been expelled in October. A staunch opponent of Benito Mussolini and Fascism, Matteotti was assassinated by Fascists, affiliated to OVRA, in June 1924. The event provoked the Aventine Secession.
Outlawed in November 1925, the PSU became active in clandestinity, as the Italian Workers' Socialist Party (Partito Socialista dei Lavoratori Italiani, PSLI). In June 1930 the PSLI re-joined the PSI.
|Chamber of Deputies|
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- Kowalski, Werner. Geschichte der sozialistischen arbeiter-internationale: 1923 - 19. Berlin: Dt. Verl. d. Wissenschaften, 1985.