The Communist Party of Fiume (Italian: Partito Comunista di Fiume – Sezione della III.a Internazionale) was instituted in November 1921, after the proclamation of the Free State of Fiume created by the Treaty of Rapallo. The Communist Party of Fiume was the smallest Communist Party in the world at the time. It was founded following the principles of the Third International, according to which each sovereign State had to have its own Communist Party organization.
After 1918 the Socialist Party of Fiume, under the lead of Samuel Maylender became the Partito Socialista Internazionale di Fiume. In 1919, a local Communist Party, was founded independently (and almost single-handedly) by Albino Stalzer in 1919, by mobilising the local dockers. Stalzer and Schneider founded also a Cooperativa dei Lavoratori del Porto, whose influence proved to be much greater than that of the Communist Party itself. In 1920 both had a difficult existence during the occupation of Fiume led by the Italian poet Gabriele D'Annunzio.
Albino Stalzer however proved instrumental in providing working class support to the autonomists of Riccardo Zanella. After the autonomist victory at the elections for the Constituent Assembly on 24 April 1921 the local Fascio staged a coup d'état. In opposition, the Camera del Lavoro (controlled by the Socialists) proclaimed a general strike, but when its leaders Antonio Zamparo and G. Holly were arrested by dictator Riccardo Gigante a cessation of the strike was proclaimed. Thanks to the Cooperativa dei Lavoratori del Porto the strike continued motu proprio, forcing the “Exceptional Government” of “Dictator” Gigante to resign and allow the entry of the Alpine troops in Fiume, as requested by the Italian plenipotentiary Carlo Caccia Dominioni.
The Cooperativa dei Lavoratori del Porto of Stalzer proved to be the main organised force of the opposition to the “dictator Gigante”, and this was the single most important action done by the leftist organisations in the Free State of Fiume. Moreover, it had clear autonomist underpinnings: what was contested was not only the fascist organisation of the putsch, but its Italian annexationist character.