MODESTO  (AP) — Federal officials are investigating CVS over tens of thousands of prescription pain killers that they say have gone missing from four of the company’s California pharmacies.

Roughly 37,000 hydrocodone tablets at CVS pharmacies in Turlock, Fairfield, Modesto and Dixon are unaccounted for, according to search-warrant affidavits reported by the Los Angeles Times on Monday.

Hydrocodone — found in such drugs as Vicodin — is one of most widely-abused prescription drugs in the U.S.

Lauren Horwood, a spokeswoman for the U.S. attorney’s office in Sacramento, told the Times CVS is facing more than 2,900 possible violations of the federal Controlled Substances Act. The violations would carry a maximum fine of $29 million, she said.

CVS spokesman Michael DeAngelis said the company regularly tells its pharmacists to maintain certain records and paperwork and recently sent them reminders.

The investigations are aimed at “assuring compliance with state and federal requirements for administrative record keeping related to invoices and inventory for controlled substances,” DeAngelis said.

The investigation stems from a case involving a CVS store in Rocklin, northeast of Sacramento, where a pharmacy worker was accused in 2012 of hiding a bottle of hydrocodone in her pants, Brian Glaudel, an investigator for the U.S. Drug Enforcement Administration, said in an affidavit.

DEA investigators discovered the other missing drugs after going over records for other CVS stores in the area, Glaudel said.

Warrants were served at each of the four CVS stores last May, Casey Rettig, a special agent in the DEA’s San Francisco office, told the Times. She declined further comment, the newspaper said.