Federal immigration agents questioned workers at about two dozen outlets of Chipotle Mexican Grill Inc. in several states Tuesday as part of an expanding probe of the company's employment practices.

Robert Luskin, an outside counsel for Chipotle, confirmed that U.S. Immigration and Customs Enforcement officials visited "20 to 25 restaurants" as part of a criminal investigation of the company. Mr. Luskin, a partner at Patton Boggs LLP in Washington, D.C., said the government had notified the company that its agents would seek...