The study, released Wednesday by left-leaning think tank Economic Policy Institute, analyzed the 17 U.S. states with the highest union membership rates. It found that the minimum wages in those states average 19% higher than the national average and 40% higher than in low-union-density states.

Earnings also tend to be higher in union-heavy states. The median annual income the 17 states examined, which include New York, Hawaii, and Alaska, was $6,000 higher than the national average.

One reason is that workers covered by a union contract earn 10.2% more than someone in the same industry with similar education, occupation, and experience, but who is nonunion. When union membership rates are high, nonunion workers tend to benefit as companies fight to remain competitive and retain workers.

Union workers are also more likely have access to employer-sponsored health benefits. More than nine in 10 unionized workers have such insurance compared with just 68% of nonunion workers.

Additionally, the study found that union-heavy states typically impose fewer restrictive voting laws. Over 70% of low-union-rate states passed at least one voter suppression law between 2011 and 2019, EPI found, Among high-union-rate states, 13 out of 17 did not pass any voter restrictions between 2011 and 2019.

This is likely a case of correlation and causation, the report said. “Unions promote economic equality and build worker power, helping workers to win increases in pay, better benefits, and safer working conditions,” says Asha Banerjee, economic analyst at EPI and co-author of the report. “The data suggest that unions also give workers a voice in shaping their communities and political representation.” 

The report also found a link between states with high union rates and health insurance. Union-dense states had relatively fewer uninsured residents— 4.5% lower—than states with low union rates. 

Research has also found that a high-density of labor unions increases political advocacy. A 2019 analysis by the National Bureau of Economic Research found that right-to-work laws, which weaken the ability of workers to unionize, reduced Democratic presidential vote shares by 3.5%. Voter turnout, the organization said, was 2% lower in right-to-work counties after passage. 

EPI’s study comes as the U.S. Senate considers the Protecting the Right to Organize (PRO) Act, which would make it easier to organize unions by protecting low-level supervisors and managers from anti-union discrimination. The PRO Act would make undocumented workers eligible for damages if their labor rights are violated, and clarify rules regarding “joint employers,” when an employee technically works for two companies.

Critics of the bill argue that it would make it more difficult for Americans to start small businesses and could force employees to join unions and pay dues against their will. 

About half of all nonunion workers say they want a union in their workplace, but only 12% of all workers are covered by a union contract.