The Justice Department is investigating UnitedHealth Group for possible criminal Medicare fraud, people familiar with the matter said. The healthcare-fraud unit of the Justice Department’s criminal division is overseeing the investigation,

The reported probe adds to a string of recent setbacks that have erased more than half, or over $300 billion, from its market value since November.

UnitedHealth Group stock fell Thursday following a report that the Justice Department is investigating the company for possible criminal Medicare fraud. The news comes only days after the struggling health insurer announced the departure of its CEO Andrew Witty due to personal reasons and suspended its full-year guidance,