The American Federation of Labor and Congress of Industrial Organizations (AFLCIO) is the largest federation of unions in the United States. It is made up of 56 national and international unions, together representing more than 12 million active and retired workers. The AFLCIO engages in substantial political spending and activism, typically in support of liberal or progressive policies.The AFLCIO was formed in 1955 when the AFL and the CIO merged after a long estrangement. Union membership in the USA peaked in 1979, when the AFLCIO's affiliated unions had nearly twenty million members. From 1955 until 2005, the AFLCIO's member unions represented nearly all unionized workers in the United States. Several large unions split away from AFLCIO and formed the rival Change to Win Federation in 2005, although a number of those unions have since re-affiliated, and many locals of Change to Win are either part of or work with their local central labor councils. The largest unions currently in the AFLCIO are the American Federation of Teachers (AFT) with approximately 1.7 million members, American Federation of State, County and Municipal Employees (AFSCME), with approximately 1.4 million members, and United Food and Commercial Workers with 1.2 million members.



The International Union, United Automobile, Aerospace, and Agricultural Implement Workers of America, better known as the United Auto Workers (UAW), is an American labor union that represents workers in the United States (including Puerto Rico) and 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 (president 1946–1970). It was known for gaining high wages and pensions for auto 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, movements of manufacturing (including reaction to NAFTA), and increased globalization.

UAW members in the 21st century work in industries including autos and auto parts, health care, casino gambling, and higher education. The union is headquartered in Detroit, Michigan. As of February 24, 2022, the UAW has more than 391,000 active members and more than 580,000 retired members in over 600 local unions, and holds 1,150 contracts with some 1,600 employers.