Labor unions — an organized group of workers in a given trade — have changed the nature of labor relations in the United States. Through collective bargaining, unions have fought to earn many workers’ rights that many of us take for granted, including weekends off, a 40-hour work week, and paid vacations.

As the global economy has become increasingly interconnected, however, foreign competition has resulted in weakening union power in much of the country. Traditional union demands for better working conditions, benefits, and pay have made it more difficult for American companies to compete in an international market, where labor is cheap. This has been especially true for the manufacturing sector — American automakers in particular. Here are five countries manufacturing more cars than America.

With plants closing amid global competition and companies demanding more leeway, the share of U.S. workers who were union members has been on the decline since the 1980s. Union membership rate nationwide declined by 1.1 percentage points in the last decade, from 11.9% in 2010 to 10.8% in 2020.

Union participation is anything but uniform across all states, and in some parts of the country membership remains at levels not seen nationally since the 1980s. Using state-level data on the share of workforces that belong to a labor union, 24/7 Wall St. identified the states with the strongest and weakest unions.

Generally, the states with where labor union participation is weakest, are those that have strong anti-union laws. Perhaps the most common and effective anti-union measures are so-called “right-to-work” laws, which prohibit companies from requiring employees to join a union or pay dues. The term “right-to-work” itself is misleading, as in no way do these laws guarantee employment for those seeking it. Instead, they erode the strength of unions, diminishing their collective bargaining power.

Kentucky is the most recent state to enact so-called right-to-work laws, joining 26 other states in 2017 — and those laws appear to be having a meaningful impact on organized labor. As recently as 2016, the share of workers in a labor union in Kentucky was 11.1%. As of 2020, unionized workers comprised only 7.5% of the workforce.

In 2018, the Kentucky American Federation of Labor and Congress of Industrial Organizations challenged the state’s right-to-work laws. However, the challenge was denied in a 4-3 decision in the state Supreme Court.

Union membership statistics are from UnionStats, a database powered by the U.S. Census Bureau’s Current Population Survey. Additional data on historical union membership and union membership by sector also came from UnionStats. Supplemental data on annual median wage came from the Bureau of Labor Statistics’ Occupational Employment Statistics program and is for 2019.