Chipotle Mexican Grill says the widespread firings in Minnesota last year over workers' immigration status totaled more than one-third of its workforce in the state.

The restaurant chain added that the lack of proper documentation for some its employees happens "without our knowledge."

In a filing with the Securities and Exchange Commission last week, the Denver-based chain said it fired 450 Minnesota workers following an audit by the U.S. Department of Homeland Security of the "work authorization documents of our restaurant employees."

Before the firings, Chipotle employed 1,200 workers in its 50 outlets, most of them in the Minneapolis-St. Paul area.

Participants in a Twin Cities protest against Chipotle had put the number of firings at 700.

Some may 'be unauthorized'

The company said in the SEC filing that the firings temporarily increased labor costs to train new employees and caused "some degree of negative publicity." Similar reviews of Chipotle employees now underway in Virginia and Washington, D.C., could affect the company's financial performance, the company added.

"Although we require all workers to provide us with government-specified documentation evidencing their employment eligibility," the filing added, "some of our employees may, without our knowledge, be unauthorized workers."

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

Some workers sued the restaurant chain, alleging that it didn't comply with a Minnesota law requiring all back pay to be distributed promptly. Greg Nammacher, secretary-treasurer of Service Employees International Union Local 26, said most of the workers suing eventually got final paychecks but not within the required 24-hour period.

Chipotle, which has 25,000 employees nationwide, has said that the suit is without merit.

In the past two years, U.S. Immigration and Customs Enforcement has audited more than 3,200 employers suspected of hiring illegal workers.

Paul Walsh • 612-673-4482