Workers' Commissions (Comisiones Obreras, CCOO). The most important and biggest union of Spain. It has more than 1.000.000 members and is the most voted union in sindical elections.

The CCOO were organized in the 1960s by the Communist Party of Spain (PCE) and workers' christian groups to fight against the dictatorship of Francisco Franco and for labor rights.

Along with other unions as Workers' Union (USO) and the Workers' General Union (UGT) summoned general strike in 1976 and carried out working fights against the dictatorship and by the labor and union rights of the workers. From years 70 it is the first union of Spain. An historical workers' leader was his General Secretary from his foundation to 1985, Marcelino Camacho , member of the Communist Party of Spain (PCE) and chosen deputy in 1977.

Between 1985 and 1997 his General Secretary was Antonio Gutiérrez . CCOO, next to the UGT, summoned three general strikes (1988, 1992 and 1994) against the economic policy of the government of Felipe González. From 1997, his General Secretary is José María Fidalgo , very criticized by the left wing of the union. CCOO summoned next to the UGT the general strike of 20 June 2002 against the reform of the insurance of unemployment of the government of José María Aznar.