More than 600 workers at popular restaurant chain Portillo Restaurant Group organized to counter management firings and calls to quit, after the business received a flurry of letters saying workers' names and Social Security numbers didn’t match.

These so-called "no match" letters are mailed by the Social Security Administration. By themselves, they say nothing about a worker's immigration status, and a mismatch can be caused by simple errors like a misspelled name. However, employers sometimes interpret them to mean a worker cannot legally work in the United States.

Portillo’s “did the right thing” after workers organized themselves, according to an email from workers’ rights organization Arise Chicago. The business backed away from calls for voluntary termination, rehired workers who were fired or left involuntarily, and paid back wages for time lost.

Mike Aponte, senior human resources manager for field operation, said in an email that the company met with employees both in the restaurants at the company’s office “to clarify and confirm that no employee has or will lose their job as a result of receiving a mismatch letter. We apologized for any confusion or concern that our initial communications caused.”

Portillo’s brought in an estimated $381 million in 2018. Boston-based private-equity firm Berkshire Partners took over Portillo’s and its real estate in a nearly $1 billion deal in July 2014. According to Berkshire Partners, the Oak Brook-based chain has nearly 60 restaurants across the U.S. and more than 6,000 employees.

Arise has fielded hundreds of messages from workers in recent weeks who’ve been improperly fired or received incorrect instructions after employers received no-match letters.

Workers from Portillo’s, assisted by Arise, created a workplace committee. Two-hundred workers delivered a petition with 600 signatures on it to Portillo’s headquarters this week. The committee is now organizing “to further improve working conditions,” the email said.