Indeed, since 1979, the percentage of U.S. private-sector workers that are unionized has fallen to 10 percent, from 34 percent. Unionization among men without a college degree has fallen to 11 percent from 38 percent in 1979. And that, in turn, has led to some pretty compelling changes in the way workers are compensated, and the power they have to influence their earnings. “Policies regarding unions and the minimum wage are going to affect the wage structure, such as how much of the value of the company makes have to be given to workers, especially low and middle pay workers,” Saez told me in a phone call earlier this month.

The idea that union decline has led to greater income inequality is supported by two new papers from Washington-area think tanks, the left-leaning Economic Policy Institute and the Center for Economic and Policy Research, a think tank founded by Dean Baker. The EPI paper by Jake Rosenfeld of Washington University, and Patrick Denice and Jennifer Laird, of the University of Washington, looks at how the decline of unions has impacted the earnings of workers who don’t belong to unions. The authors find that the presence of unions significantly affects the wages of non-union workers, especially those without a college degree. Non-union men without a high school diploma would be experiencing weekly wages that were 9 percent higher if union density had remained at 1979 levels, the authors estimate. That translates to $3,172 a year. Non-union men without a bachelor’s degree would have seen weekly wages that were 8 percent higher with union density at 1979 levels; weekly wages for all private-sector men would have been 5 percent high with that union density.

The authors calculate how high wages would have been by using current wages as a benchmark and employing standard regressing wage equations to estimate what wages would have been had they remained on their trajectory before union density fell. They accounted for job loss and automation in an area by also calculating demand—or the lack of it—in certain industries. They found decline in non-union wages even in industries such as construction and trucking—which saw unionization decline—even though those jobs can’t be outsourced.

In the past, non-union employers would often be forced to keep wages on par with wages at unionized plants. If they didn’t, they’d lose workers to unionized jobs. Employers also feared that if they didn’t keep wages and benefits high, workers would decide to unionize, which would give companies less control in setting pay and benefits.

When unions are strong, they can advocate for rules and regulations that help all workers. European countries also experienced waves of globalization and increased reliance on technology, but their workforce hasn’t seen the same declines in union membership or non-union wages, the report found.“It’s not inevitable that you see staggering wage losses and jobs decline” in the 21st century, Rosenfeld said.