The U.S. Department of Justice's criminal healthcare-fraud unit is investigating UnitedHealth Group's Medicare billing practices. The probe, which has been ongoing since at least last summer, focuses on how UnitedHealth deployed doctors and nurses to collect diagnoses that potentially increased Medicare payments. Prosecutors have questioned former UnitedHealth employees, including doctors, about these practices. Meanwhile, UnitedHealth reportedly sold some businesses to private equity firms late last year to meet Wall Street earnings targets. The company has also been accused of aggressively threatening legal action against doctors and media outlets to silence critics. Lawmakers have called for the Justice Department to broaden its investigation into UnitedHealth's operations, emphasizing the need for the company to improve access to care and timely payments to providers.