trade-union federation that was the largest in Japan. Sōhyō was founded in 1950 as a democratic trade-union movement in opposition to the communist leadership of its predecessor organization. It rapidly became the most powerful labour organization in postwar Japan and formed close ties with the Japan Socialist Party. The major affiliates of Sōhyō included unions of government workers, teachers, national railway workers, communications workers, and metal-industry workers. Under Japanese labour law, workers who were employed in local or national government did not have formal bargaining power or the right to strike; workers who were employed in public corporations had bargaining rights but not the right to strike. Because the majority of Sōhyō membership was made up of such workers, the union frequently used political action in place of economic action. Sōhyō's best-known political tactic, begun in 1955, was the annual spring struggle, which was an intensive campaign of street demonstrations, mass meetings, and other pressure tactics.

In 1989 Sōhyō dissolved itself, and the majority of its membership was absorbed in the recently formed Rengō (q.v.), a trade-union confederation that effectively unified the noncommunist segments of organized labour in Japan.