The Justice Department is probing diagnoses and practices that triggered extra payments to UnitedHealth’s Medicare Advantage plans, people familiar with the matter say.

The health insurance giant has called a new report from WSJ “misinformation,” but investors may not be so sure. Shares were down about 9% early Friday. UnitedHealth Group, America’s largest insurer, is facing yet another crisis.

UnitedHealth Group (UNH) tanked as much as 12% on Friday, Feb. 21 following reports that the Department of Justice has launched an investigation into the healthcare services firm. The DOJ scrutiny is centered on the company’s Medicare billing practices,