The Italian Syndicalist Union (Italian: Unione Sindacale Italiana; USI) is an Italian anarcho-syndicalist trade union. Established in 1912 by a confederation of "houses of labour", the USI led a series of general strikes throughout its early years, culminating with the Red Week insurrection against the Italian entry into World War I. During the Biennio Rosso, the USI was at the forefront of the occupation of factories, which saw hundreds of workplaces throughout the country brought under the control of workers' councils. The USI also led the establishment of the International Workers' Association (IWA), which became the main international organisation of anarcho-syndicalist trade unions.
After the rise of Italian fascism, the USI was banned and its members were either arrested, driven underground or forced into exile. By the late-20th century, the USI was eventually reconstituted and once again involved itself in radical strike actions. Expelled from the IWA in 2016, together with the Spanish CNT and German FAU, it established the International Confederation of Labour (ICL), a new international of anarcho-syndicalist trade unions.
