Chipotle Mexican Grill is being subpoenaed by the U.S. Attorney's Office in California.

The investigation

The subpoena was served to the restaurant last month and relates to the illnesses that started at several of the chain restaurants in late October and early November, the company said in a filing.

The lawsuit, brought on the by the U.S. Attorney's Office for the Central District of California, asks the company to produce documents from its Simi Valley, California, restaurant.

Chipotle's been dealing with the E. coli outbreak that started in late October. Then a location in Boston had a norovirus outbreak in December, which left more than 130 people sick. By the end of 2015, more than 500 people had gotten sick after eating in a Chipotle restaurant, according to Food Safety News.

 

"No, I will not come back," one Boston College student told WBZ-TV.

The highly publicized illnesses have sent sales and stocks plummeting.

Chipotle's stock has dropped some 300 points since its peak three months ago before the illnesses were reported.