President Franklin D. Roosevelt signed the National Labor Relations Act (also called the Wagner Act), creating a federal policy that protected workers’ rights to organize and bargain collectively. It also set up the National Labor Relations Board (NLRB) to enforce those rights. This legal foundation helped industrial union organizing grow quickly in the mid-1930s.
Union leaders led by John L. Lewis announced a new group inside the American Federation of Labor (AFL) to promote industrial unionism—organizing all workers in a plant or industry, not only skilled trades. The move highlighted a widening split with the AFL’s traditional focus on craft unions. This announcement is commonly treated as the start of the CIO’s rise.
As the new committee pushed mass-production organizing, conflict with the AFL leadership intensified. The AFL suspended unions associated with the industrial-union drive, showing that the dispute was no longer only about tactics but about control and structure in the labor movement. This set the stage for the CIO’s independent national role.
Workers at General Motors plants in Flint, Michigan used a sit-down strike—occupying the workplace—to stop production while preventing strikebreakers from entering. The strike ended with General Motors recognizing the United Auto Workers (UAW). The victory became a model for fast-growing CIO-style organizing in mass-production industries.
U.S. Steel reached a landmark agreement with the Steel Workers Organizing Committee (SWOC), a CIO organizing arm in steel. The deal showed that even very large corporations could be brought into collective bargaining, and it encouraged further organizing across the steel industry. It also raised the stakes for companies that still refused to recognize unions.
After several major steel employers resisted union recognition, the CIO’s SWOC launched the Little Steel strike. The conflict spread across many mills and became one of the most violent labor disputes of the 1930s. The strike ended without winning union recognition, showing both the CIO’s ambition and the limits of organizing when employers and local authorities fought back.
At a convention in Pittsburgh, the organization formalized its separation from the AFL. It adopted a constitution and the name Congress of Industrial Organizations (CIO), and it elected John L. Lewis as president. From this point, the CIO operated as a competing national labor federation centered on industrial unions.
The United Steelworkers (USW) was created by merging the earlier craft-based steel union with the CIO’s organizing committee structure. This consolidated steelworker representation into a large industrial union. It strengthened the CIO’s influence in a core sector of U.S. heavy industry.
As World War II ended, many unions sought wage increases after years of wartime restrictions. Major strikes spread across industries, pushing employers, unions, and government to renegotiate the postwar rules of labor relations. These conflicts helped define what collective bargaining would look like in the mid-century economy.
The CIO began Operation Dixie, a major campaign to unionize Southern manufacturing, especially textiles. Leaders hoped higher unionization would raise wages and reduce employer incentives to shift production to low-wage regions. The effort faced strong obstacles, including Jim Crow segregation, employer resistance, and a hostile political climate.
Congress enacted the Labor Management Relations Act (Taft–Hartley), amending the Wagner Act and adding new limits on union tactics and organizing. The law reflected a shift in national politics toward restricting labor’s power after the war. It made organizing drives and strike strategy more legally complex for CIO unions.
At its 1949 national convention in Cleveland, the CIO strengthened anti-communist rules and empowered expulsions of unions and leaders seen as aligned with Communism or Fascism. Several unions’ charters were revoked, and new “replacement” unions were organized in some industries. The purge changed internal CIO politics and affected its public image during the early Cold War.
After Philip Murray’s death, CIO delegates elected Walter Reuther, president of the UAW, as the federation’s new leader. Reuther pushed for an image of unions as democratic and firmly anti-communist, while also promoting social reforms allied with labor’s agenda. His leadership also supported renewed efforts toward labor unity with the AFL.
After years of negotiation, the AFL and CIO merged to form the AFL–CIO, ending a long period of competition and “raiding” (trying to organize the same workplaces). The merger aimed to unify strategy in collective bargaining and politics during the Cold War era. It marked the CIO’s endpoint as a separate federation and set a new structure for U.S. organized labor.
Formation and Rise of the Congress of Industrial Organizations (CIO) (United States, 1935–1955)