The US Justice Department has launched a civil fraud investigation into the organization's Medicare billing practices.

UnitedHealth Group shares tumbled Friday on a report that the U.S. Department of Justice has started an investigation into the health care giant's Medicare billing practices.

The Wall Street Journal says the U.S. Justice Department in recent months has launched an investigation into UnitedHealth Group’s billing practices to see if the company fraudulently used diagnosis data to trigger extra Medicare Advantage payments.