Sen. Chuck Grassley, chairman of the Senate Judiciary Committee, sent UnitedHealth Group Chief Executive Andrew Witty a letter demanding detailed information on the company’s Medicare billing practices Monday.

U.S. Senator Chuck Grassley requested detailed information on UnitedHealth's Medicare billing practices in a letter to CEO Andrew Witty, amid reports suggesting the insurer may have leveraged billing rules to its advantage.

Hi, it’s John in New York. I’ve spent years following a story about how whistleblowers alleged systematic fraud at private Medicare Advantage plans. A reported investigation at one of the biggest companies in that business jolted investors last week.