A Waterloo, Iowa, hospital paid $4.5 million to settle a claim that they improperly used Medicare to pay five physicians. They are among the highest paid doctors in the country.

The Covenant Medical Center allegedly paid the doctors above market value which disqualifies them from receiving Medicare dollars.

“It’s the combination of the referrals without being fair-market value and commercially responsible…when there’s improper financial incentives potentially at play there,” said U.S. Attorney Matt Dummermuth

The investigation by the Justice Department and the Department of Health and Human Services began in 2005.