Chipotle is now the subject of a federal criminal investigation

Chipotle is the subject of a criminal investigation into a norovirus outbreak linked to one of its restaurants.

In an SEC filing on Wednesday, the company said it was served with a federal grand jury subpoena in connection with an official criminal investigation being conducted by the US Attorney's Office for the Central District of California and the US Food and Drug Administration's Office of Criminal Investigations.

"The subpoena requires us to produce a broad range of documents related to a Chipotle restaurant in Simi Valley, California, that experienced an isolated norovirus incident during August 2015," Chipotle says in the filing. "We intend to fully cooperate in the investigation. It is not possible at this time to determine whether we will incur, or to reasonably estimate the amount of, any fines, penalties or further liabilities in connection with the investigation pursuant to which the subpoena was issued."

A federal grand jury subpeona means prosecutors are gathering evidence to present it to a grand jury, which will decide if there is enough evidence to indict Chipotle on unspecified charges.

We've reached out to Chipotle, as well as the US Attorney's Office for the Central District of California for more information.