Which U.S. labor federation merged with the AFL in 1955 to create the AFL–CIO?

The Congress of Industrial Organizations merged with the AFL in 1955 to create the AFL–CIO.

The CIO began in 1935 as the Committee for Industrial Organization inside the American Federation of Labor. It promoted industrial unionism, organizing workers across an entire industry rather than limiting membership to a particular skilled trade.

The CIO became independent after a dispute with the AFL and was renamed the Congress of Industrial Organizations in 1938. It organized major unions in industries such as automobiles, steel, rubber, and electrical manufacturing.

The merger took place on December 5, 1955. The resulting AFL–CIO became the largest federation of unions in the United States. The CIO is sometimes confused with the AFL itself, but the two organizations represented different organizing strategies before their merger.