"Its definitely on the rise nationally because of the economic crisis," said Ted Smukler, public policy director at Interfaith Worker Justice in Chicago.
"Employers are desperate to shave corners when their profits are going down," Smukler told USA Today Monday.
In Austin, Texas, the Workers Defense Project said complaints more than doubled in the first half of the year.
Complaints also rose sharply in the first half of the year at the Chicago Working Hands Legal Clinic, Executive Director Chris Williams said.
Williams said the majority of complaints come from immigrants.
Illegal immigrants fear deportation, but they are still covered by minimum wage and overtime laws, the U.S. Labor Department said.
"We do a lot of work with workers at temporary staffing agencies, people who work maybe 32 hours but they're only getting paid for 26," Williams told the newspaper.