Chipotle Mexican Grill said Wednesday that it was subpoenaed by the U.S. Attorney’s Office for the Central District of California for a criminal investigation. The probe is related to a norovirus outbreak that occurred in August at a restaurant in Simi Valley, California.

The popular burrito chain has been asked to hand over “a broad range of documents” about that location’s operations and said in a statement that it intends to fully cooperate with authorities. The Denver-based chain also announced nationwide, same store sales suffered a staggering blow in the fourth quarter, dropping 14.6 percent. The company’s stock was down 2.51 percent shortly after the announcement.

In Simi Valley, at least 98 customers and 17 employees of Chipotle were sickened by norovirus on Aug. 18 and 19. An investigation conducted by local health inspectors shortly after the outbreak found a series of code violations, including equipment that was connected directly to the sewer system, dirty restrooms, insects and employees who lacked a required food handler certification.

Once that situation was resolved, the chain’s food safety troubles continued. An E. coli outbreak sickened 53 customers across nine states in late October and early November. In December, at least 153 customers fell ill from an unrelated norovirus outbreak after eating at a Chipotle in Boston. The U.S. Centers for Disease Control and Prevention is currently investigating another potential E. coli outbreak from the restaurant’s locations in five other states that occurred in November.

The company estimates it has spent between $14 and $16 million to replace food at restaurants affected by the outbreaks, set up a new system of testing and increase marketing amid the crises. The company has factored in expenses for expected legal claims.