The company has said in regulatory filings that investigations, audits and reviews by a dozen different government agencies are currently underway.

Shares of UnitedHealth Group tumbled 16% in intraday trading Thursday, leading S&P 500 decliners, on a report that the U.S. Department of Justice is investigating the embattled health insurance provider for possible criminal Medicare fraud.

UnitedHealth Group, one of America’s largest health insurers, is facing a storm of challenges—from a criminal investigation to a leadership shake-up—that have rattled markets and erased billions in shareholder value.