Senator Charles Grassley has requested information from three nonprofit North Carolina hospital to determine whether they are passing along to patients savings from their participation in a federal drug-discount program, The Charlotte Observer and the Raleigh News & Observer report.

In a letter e-mailed Friday to the heads of Carolinas Medical Center, Duke University Health System, and UNC Hospitals, the Iowa Republican—a leading congressional watchdog of charities’ fiscal practices—said the institutions’ drug savings appear to be boosting “bottom line operating margins” rather than benefiting patients.

The senator cited a recent investigation by the two North Carolina newspapers into major markups for chemotherapy drugs at large medical systems in requesting data on their savings from the U.S. government’s 340B program and how they have used the funds.

More than 40 hospitals across the state take part in 340B, which requires pharmaceutical firms to give institutions that serve needy populations big discounts on outpatient drugs. The hospitals contacted by the senator said they would cooperate with his office.