Photo Credit: Kheel Center, Cornell University.

Our data on strikes comes primarily from government sources, including yearly reports from the Bureau of Labor Statistics (BLS) and data from the Federal Mediation and Conciliation Service (FMCS), as well as some union reported strike statistics. We follow the practice of the BLS reports from early decades, where the term "strike" is defined as any work stoppages, including strikes and lockouts (the vast majority of disputes were strikes). 

In the early 1900s, worked faced many constraints to striking, including the possibility of injunctions and violence. The National Labor Relations Act, passed in 1935, provided that most private sector employees may engage in work stoppages or refusals to work during labor disputes or unfair labor practice strikes (section 7). Generally, subsequent legislation, court decisions, NLRB case law, and clauses in collective bargaining contracts imposed constraints on when, for what purposes, and under which circumstances workers may strike. Workers excluded from the NLRA, including public sector workers, farm workers, and others, face different and shifting legal constraints.