Medicare Advantage, which has long enjoyed support from Republicans, has faced growing bipartisan scrutiny. Among the biggest players in the business are UnitedHealth Group, Humana and Elevance Health.

Lawmakers and government investigators have been probing how insurers’ billing practices have contributed to Medicare Advantage costs. A congressional watchdog found Medicare Advantage costs the federal government more than traditional Medicare, partly because of insurers’ billing practices. The insurers are paid more to cover enrollees who have more health conditions, and they can boost their reimbursement by recording more diagnoses.