The Justice Department has reportedly launched a probe into the billing practices of UnitedHealth's Medicare.

The Wall Street Journal reports the probe is a civil fraud investigation that will look into whether the billing practices have led to resulting in extra payments to Medicare Advantage plans for recording diagnoses.

Stock prices for the healthcare conglomerate decreased by about 9% following the release of the report Friday.

UnitedHealth says th report has "misinformation."

As medical costs continue to rise around the U.S., the company's margins are feeling the pressure, according to the Yahoo Finance outlet.

The DOJ has a pending lawsuit against UnitedHealth over Medicare Advantage that will likely go to trial in October.