A group of workers that Chipotle Mexican Grill fired for being illegal immigrants sued the restaurant chain on Thursday, alleging that it didn't comply with a Minnesota law requiring all back pay to be distributed promptly.

Last month, Chipotle said it fired a substantial number of its 1,200 Minnesota workers starting in December, after a federal immigration audit found some of them to be illegal immigrants.

Participants in a protest against the firings put the number at 700. The company wouldn't say how many there were, but a source close to the investigation put the number closer to 350.

Up to 75 of those former workers filed a class-action suit alleging that Chipotle violated the Minnesota Payment of Wages Act, said Greg Nammacher, secretary-treasurer of Service Employees International Union Local 26.

The law says that wages due at the time of an employee's discharge are to be paid within 24 hours. If they're not, as a penalty to an employer, employees are eligible to be paid their average daily wage for up to 15 days, as well as any wages still owed.

Nammacher said that most of the workers in the suit eventually got their final paychecks, but not within the 24-hour period mandated by the law.

Chipotle said in a statement that the lawsuit has no merit. "We have paid every employee everything that they were owed including wages, accrued vacation, and bonuses. We provided contact information to employees so anyone who did not feel they were paid everything they were owed could contact us, and we have heard from only a few employees."

After the U.S. Immigration and Customs Enforcement office singled Chipotle out for review, the company said it gave workers one-on-one opportunities to provide documents that could prove they were legally able to work in the United States. Supporters of the fired workers claim that they were fired without much explanation and without enough time to provide documentation.

Mike Hughlett • 612-673-7003