UnitedHealth Group shares tumbled early 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 said federal officials have launched a civil fraud investigation into how the company records diagnoses that lead to extra payments for its Medicare Advantage plans.

UnitedHealth Group Inc. shares fell early Friday after a report that the US Justice Department has begun investigating the insurer’s billing practices in recent months.

The U.S. Justice Department has launched an investigation into UnitedHealth's Medicare billing practices in recent months, the Wall Street Journal reported on Friday, citing people familiar with the matter.