President Franklin D. Roosevelt signed the National Labor Relations Act (the Wagner Act), creating rules that protected many private-sector workers’ right to join unions and bargain collectively. It also created the National Labor Relations Board (NLRB) to run union elections and address unfair labor practices. These changes helped set the stage for rapid growth of industrial union organizing in the late 1930s.
After disputes inside the American Federation of Labor (AFL) over how to organize mass-production industries, union leaders led by John L. Lewis announced a new coordinating group: the Committee for Industrial Organization. The committee promoted industrial unionism, meaning one union for all workers in an industry rather than separate craft unions. This step marked the beginning of what became the CIO.
Workers in Flint, Michigan used a sit-down strike—occupying GM plants—to demand recognition of the United Automobile Workers (UAW). The strike ended with GM recognizing the union, helping the UAW grow quickly. The victory became a widely noted example of how industrial organizing could succeed in large manufacturing firms.
The AFL’s executive council moved from suspension to expulsion of CIO-aligned unions from many AFL bodies, deepening the split inside organized labor. This made it harder to keep the industrial-union drive “within” the AFL. The conflict pushed the Committee for Industrial Organization toward building an independent federation.
U.S. Steel signed a key recognition agreement with the Steel Workers Organizing Committee (SWOC), the CIO’s steel organizing arm. This agreement helped establish collective bargaining in a major “mass production” industry and encouraged further organizing. It also shaped the following fights with smaller steel companies that refused to recognize the union.
During the Little Steel strike, Chicago police fired on demonstrators near Republic Steel, killing 10 people and injuring many others. The episode became a symbol of the violence surrounding some anti-union resistance in the late 1930s. It also influenced public and political debates about labor rights and policing of strikes.
At its first constitutional convention in Pittsburgh, the organization formally reconstituted itself as the Congress of Industrial Organizations (CIO). This confirmed a full break from the AFL after years of conflict over organizing strategy and jurisdiction. The CIO now operated as an independent national federation focused on industrial unions.
John L. Lewis stepped down, and Philip Murray was elected president of the CIO. Under Murray, the CIO emphasized building stable national unions and expanding collective bargaining coverage. The leadership change also mattered politically as the CIO navigated World War II labor policy and postwar conflicts.
The Steel Workers Organizing Committee (SWOC) was reorganized into the United Steelworkers of America, creating a permanent union structure for steelworkers. This helped standardize bargaining across employers and strengthened the CIO’s position in heavy industry. Steel became one of the central pillars of postwar industrial unionism.
The CIO established the CIO Political Action Committee (CIO-PAC) to coordinate election activity and support candidates aligned with labor goals. This was an important shift toward organized, nationwide political campaigning by a labor federation. The PAC became especially significant in debates over postwar labor law and union rights.
The CIO launched Operation Dixie, a major campaign to organize Southern industries, especially textiles. Leaders aimed to raise wages in the South and reduce employers’ ability to undercut union standards elsewhere. The effort faced strong resistance—including Jim Crow segregation—and fell short of its goals, limiting CIO growth in the region.
Congress enacted the Taft–Hartley Act over President Truman’s veto, amending federal labor law to restrict certain union practices and allow states to pass “right-to-work” laws. It also required union officers to sign non-communist affidavits for unions to access NLRB processes. The law reshaped the CIO’s strategy by increasing legal and political pressure on organizing and strikes.
At a national convention in Cleveland, CIO delegates approved rules barring communists and fascists from leadership and voted to revoke charters of several left-led unions. This “purge” changed the CIO’s internal politics and reduced tensions with anti-communist lawmakers and some AFL leaders. It also caused major losses in membership and organizing capacity in certain industries.
After years of rivalry and renewed negotiations, the AFL and CIO joined together in a merger convention in New York City, creating the AFL–CIO. The merger aimed to reduce competition between unions and present a united labor front in national politics and bargaining. It marked the end of the CIO as a separate federation and closed the 1935–1955 era of split national labor organization.
Congress of Industrial Organizations (CIO) — formation to postwar merger (1935–1955)