Medicare practices sent the stock diving Thursday to a five-year low. The Justice Department is looking into potential Medicare fraud by the health insurer, according to a report by the Wall Street Journal,

UnitedHealth Group (UNH) shares cratered more than 13% Thursday morning after The Wall Street Journal reported that the Department of Justice is conducting a criminal investigation into the company’s Medicare billing practices.

UnitedHealth Group shares fell nearly 6% in premarket trading on Thursday, after the Wall Street Journal reported that the U.S. Department of Justice was investigating the company for potential Medicare fraud.