The United Auto Workers (UAW), fully named International Union, United Automobile, Aerospace and Agricultural Implement Workers of America, is an American labor union that represents workers in the United States and southern Ontario, Canada. It was founded as part of the Congress of Industrial Organizations (CIO) in the 1930s and grew rapidly from 1936 to the 1950s. The union played a major role in the liberal wing of the Democratic Party under the leadership of Walter Reuther. It was known for gaining high wages and pensions for automotive manufacturing workers, but it was unable to unionize auto plants built by foreign-based car makers in the South after the 1970s, and it went into a steady decline in membership; reasons for this included increased automation, decreased use of labor, mismanagement, movements of manufacturing, and increased globalization. After a successful strike at the Big Three in 2023, the union organized its first foreign plant (VW) in 2024.

The Congress of Industrial Organizations (CIO) was a federation of unions that organized workers in industrial unions in the United States and Canada from 1935 to 1955. Originally created in 1935 as a committee within the American Federation of Labor (AFL) by John L. Lewis, a leader of the United Mine Workers (UMW), and called the Committee for Industrial Organization. Its name was changed in 1938 when it broke away from the AFL. It focused on organizing unskilled workers, who had been ignored by most of the AFL unions.