Final answer:
The strength of labor unions in the US has waned since the 1980s, significantly impacted by events like the PATCO strike in 1981 and ensuing legislation which made it challenging for unions to maintain membership and influence.
Step-by-step explanation:
The strength of labor unions in the United States has notably declined since about 1980. In 1981, a significant event in labor union history occurred when the Professional Air Traffic Controllers Organization (PATCO) went on strike, seeking better working conditions.
This action was in line with the union's perspective that striking was a legitimate way to achieve improvements not just for workers but also for public safety. President Reagan's response to the PATCO strike, which was to fire the twelve thousand striking federal air traffic controllers, had a profound effect on labor relations in the US. It set a precedent for employers to replace striking workers rather than negotiate, which contributed to a new era in labor relations and influenced the decline in union membership levels.
Historically, pro-union laws like the National Labor Relations Act of 1935 had encouraged union formation by ensuring workers' rights to organize. However, subsequent legislation such as the Taft-Hartley Act of 1947, which allowed workers to opt out of unions, created a legal environment less conducive to union growth.
Changes in the economic structure, with job growth shifting from manufacturing (where unions were traditionally stronger) to service sectors where unions had less presence, further compounded the decline in union strength. Additionally, international differences in labor laws suggested that the US legal climate might be less supportive of unionization compared to other countries.