MANY economists say the stubbornly high jobless rate and the declining power of labor unions are also important factors behind the declining wage share, reducing the leverage of workers to demand higher wages. Unions represent just 7 percent of workers in corporate America, one-quarter the level in the 1960s.

“There are very few occupations or industries where unions are strong enough where they can set standards,” says Lawrence Mishel, president of the Economic Policy Institute. “There are no standards being set, so companies can push down on wages for all workers, union and nonunion alike.” When the Detroit automakers secure two-tier contracts, that enables them to pay new hires $16 an hour, far less than the $28 an hour earned by longtime workers. This also pushes down labor’s share.

Pamela Waldron, a cashier at a KFC restaurant in Manhattan, earns $7.75 an hour after eight years on the job and says she last received a raise in 2007. “Being here eight years, I think I should be getting more,” she said. “You can fight for a raise, but I don’t think you’re going to get it.”

It is often thought that college graduates can escape these unfortunate wage trends. But college graduates — hit by the bursting of the tech bubble in the late 1990s and then by the deep recession — have been hit hard, too. Seventy percent of the nation’s college grads have had their after-inflation hourly wages decline since 2000, according to the Economic Policy Institute, with the typical graduate experiencing a 3.1 percent decline.

Jared Bernstein, who served in the Obama administration as executive director of the White House Task Force on the Middle Class, said many steps should be taken to increase labor’s income share, including raising the minimum wage, pushing down the jobless rate, enacting laws that make it easier for workers to unionize and increasing wage subsidies for those on the bottom. He also said the federal government, in spending hundreds of billions on health care, might insist that providers pay home-care aides or lab technicians $20 an hour rather than $10. “There’s no reason why a lab technician with a few years of community college shouldn’t be able to find her way into some segment of the middle class,” he said.

Professor Katz of Harvard said it would make sense to create a more progressive tax system when corporations and the top 1 percent are commanding more of the economic pie. He said those on top should agree to some redistribution and to invest in the next generation.

“We’ll end up with a larger pie, and they’ll be better off — even though they may think it clashes with their own self-interest,” he said.