Fact: The unionization rate for the U.S. workforce in 2015 was 11.1 percent in 2015, the most recent low point in a long, steady decline in union penetration since there was a 20.1 percent representation rate in 1983.

Fact: One of the major factors holding back U.S. economic expansion is the dismal growth of U.S. wages, for both union and nonunion workers. Real average U.S. weekly wages have only risen 0.9 percent during this decade.

Not enough politicians, pundits or economists connect those two facts, says a new report by the Economic Policy Institute (EPI), and their failure to do so is to the detriment of the U.S. economy.

"Rebuilding our system of collective bargaining is an important tool available for fueling wage growth for both low- and middle-wage workers and ending the era of persistent wage stagnation," concludes the EPI, a labor-backed think-tank.

Pay for private-sector workers has barely budged over the past three and a half decades, taking the inflation rate into account. In fact, for men in the private sector who lack a college degree and do not belong to a labor union, real wages today are substantially lower than they were in the late 1970s.

A report by the EPI released Aug. 30 titled "Union decline lowers wages of nonunion workers - the overlooked reason why wages are stuck and inequality is growing," makes a direct connection between lower union penetration and lower pay for workers.

"In the debates over the causes of wage stagnation," wrote EPI researchers Jake Rosenfeld, Patrick Denice, and Jennifer Laird, "the decline in union power has not received nearly as much attention as globalization, technological change, and the slowdown in Americans’ educational attainment. Unions, especially in industries and regions where they are strong, help boost the wages of all workers by establishing pay and benefit standards that many nonunion firms adopt."

But that boost to nonunion pay has been slackening. Private sector union representation - 6.7 percent - is also at an all-time low and is even worse than the public sector rate. The scant number of private sector nonunion workers is no longer enough to lift pay scales up for others. "This union boost to nonunion pay has weakened as the share of private-sector workers in a union has fallen from 1 in 3 in the 1950s to about 1 in 20 today," the EPI researchers said.

A few key findings from their report include::

*For nonunion private-sector men, weekly wages would be an estimated 5 percent ($52) higher in 2013 if private-sector union density (the share of workers in similar industries and regions who are union members) remained at its 1979 level. For a year-round worker, this translates to an annual wage loss of $2,704. For the 40.2 million nonunion private-sector men the loss is equivalent to $2.1 billion fewer dollars in weekly paychecks, which represents an annual wage loss of $109 billion.

*The effects of union decline on the wages of nonunion women are not as substantial because women were not as unionized as men were in 1979. Weekly wages would be approximately 2 to 3 percent higher if union density remained at its 1979 levels for all nonunion women; nonunion, non–college graduate women, and nonunion women with a high school diploma or less education.

*Declines in union percentage have resulted in weekly wage declines of $52.39 for nonunion men and $13.80 for nonunion women.

*As a large body of work documents, unions raise the wages of their members, especially private-sector members, relative to nonunion workers. The percent by which their wages exceed nonunion wages is called the “union wage premium.” Union decline means that many workers today do not enjoy the wage premium attached to membership that they would have when organized labor remained strong. Thus deunionization—the erosion of the share of workers who belong to a union—has directly contributed to wage stagnation by reducing the fraction of the workforce receiving the union wage premium.

*The EPI contends that unions, especially in industries and regions where they are strong, have indirect effects on wages, helping to establish pay and benefit standards that many nonunion firms adopt.

However the cumulate effects are still sizable. For 32.9 million full-time nonunion women working in the private sector, weekly pay would be a total of $461 million more (and roughly $24.0 billion more per year) in 2013 if unions had remained as strong as they were in 1979.