Unione Sindacale Italiana

Unione Sindacale Italiana (USI; Italian Syndicalist Union or Italian Workers' Union) was an Italian anarcho-syndicalist trade union. It was the Italian section of the International Workers' Association (IWA; Associazione Internazionale dei Lavoratori in Italian or AIT - Asociación Internacional de los Trabajadores'' in the common Spanish reference), and the name of USI was also abbreviated as USI-AIT.

The most left-wing camere del lavoro adhered in rapid succession to the USI, and it engaged in all major political battles for labor rights - without ever adopting the militarist attitudes present with other trade unions. Nonetheless, after the outbreak of World War I, USI was shaken by the dispute around the issue of Italy's intervention in the conflict on the Entente Powers' side. The problem was made acute by the presence of eminent pro-intervention, national-syndicalist voices inside the body: Alceste De Ambris, Filippo Corridoni, and, initially, Giuseppe Di Vittorio. The union managed to maintain its opposition to militarism, under the leadership of Armando Borghi and Alberto Meschi and pro-war elements were expelled from the USI in 1914. In response, pro-intervention members established the Fascio Rivoluzionario d'Azione Internazionalista and joined the Fasci d'Azione Rivoluzionaria, a new political movement attempting to unite all pro-war leftist forces; many of their members would later establish the Unione Italiana del Lavoro (UIL) in 1918, a national-syndicalist alternative to the USI.