Two U.S. lawmakers are quizzing federal officials, wanting to know why there aren’t more skilled nursing providers in a program for under performers.

Sen. Robert Casey Jr. (D-PA) and Sen. Patrick Toomey (R-PA) spelled out their concerns in a letter to the Centers for Medicare & Medicaid Services chief Monday, which follows a news investigation shedding light on abuse at Pennsylvania nursing homes,. They’re curious why less than 1% of the nation’s 15,000-plus facilities are taking part in the Special Focus Facility Initiative, which works to bolster care at persistently underperforming providers.

They’re particularly curious to get their hands on a “secret list” of nursing facilities that are candidates for the program, but have not been given the special designation.

“We know which nursing homes participate in the Special Facility Focus program, but we don’t know anything about those not chosen,” Casey said, according to Penn Live. “Pennsylvanians and families across the country deserve to know which nursing homes performed badly enough to warrant a nomination and whether or not those facilities are improving.”

The senators’ ire stems from a recent investigative series, published by the news website, which found that a chain of Pennsylvania nursing homes has been mired in problems. Three SNFs highlighted in the series are on the special focus facilities list.

Casey — who also brought up his concerns during a Senate hearing on nursing home abuse Wednesday — and Toomey posed several questions to CMS on the program in the letter. They’re demanding answers by March 27 and are also angling for a staff briefings on the matter.