Sen. Gary Peters said he was concerned that emergency medicine staffing companies “may be engaging in cost-saving measures at the expense of patient safety and care.”

A Senate committee has asked three major private-equity firms for information on how they run or staff hospital emergency departments to see if private equity’s management of a large share of the nation’s ERs has harmed patients.

Led by its chairman, Sen. Gary Peters, D.-Mich., the inquiry by the Homeland Security and Governmental Affairs Committee centers on three of the nation’s largest private-equity firms: Apollo Global Management, the Blackstone Group and KKR. According to the information requests, Peters’ staff conducted interviews with over 40 emergency department physicians who expressed “significant concerns” about patient safety and care resulting from the aggressive practices of private-equity firms in the arena. Those practices include improper billing, retaliation and anti-competitive activities, the committee’s letters to the companies said.