The U.S. Attorney's Office for the District of New Jersey sought various documents from Select Medical Holdings Corp. to assess whether the company's contract therapy division was in compliance with Medicare's skilled nursing facilities billing requirements.

The company operated the division through a subsidiary which was later sold.

Select Medical is producing documents in response to the subpoena, which was received in May, and plans to fully cooperate with the investigation. The company said it is unable to predict the timing and outcome of this matter.