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Activists protest in March outside of a McDonald's restaurant in Oakland, California.  - 

A Labor Department-commissioned study found 3.5 to 6.5 percent of wage and salary workers in California and New York are paid less than minimum wage.

"More than 2 million workers are not paid the minimum wage every week, and that’s out of 150 million workers in the workforce," says Steven Greenhouse, labor and workplace reporter for the New York Times. 

The study is based on 2011 data, when the minimum wage in both states was lower than they are now. The study says 11 percent of low-wage workers suffered minimum-wage violations.

"The industry with the worse minimum-wage violations is leisure hospitality, meaning restaurants and hotels," Greenhouse says. "followed by healthcare, education and retail."

Some workers are denied overtime pay while some employers simply do not pay their employees for the full number of hours that they worked, which results in them being paid less than minimum wage.

"I've done front-page stories for the Times about companies that go into the computer to erase hours that people work," says Greenhouse. "Oftentimes, workers don't even recognize that because they don't do a very good job keeping track of how many hours they work."

Follow Kai Ryssdal at @kairyssdal