The Federal Trade Commission is seeking information on the role played by drug distributors and other companies that purchase medicines for US hospitals over a shortage of generic drugs like chemotherapies and antibiotics, it said Wednesday.

The public information request by the agency and the Department of Health and Human Services comes on the back of a shortage of crucial drugs like chemotherapies over the last year, which has forced hospitals to ration them to patients.

“For years Americans have faced acute shortages of critical drugs, from chemotherapy to antibiotics, endangering patients,” said FTC Chair Lina Khan.

“Our inquiry requests information on the factors driving these shortages and scrutinizes the practices of opaque drug middlemen.”

The FTC will seek information about drug distributors and hospital purchasing groups and their contracting practices, market concentration and compensation.

It will examine if these companies have misused their market power to push down prices of generic drugs so much that some manufacturers cannot profit and have stopped production, in turn causing the shortages.

The FTC and HHS statement did not name the companies.

Cencora, Cardinal Health and McKesson are the big drug distributors in the United States, while Vizient, Premier and HealthTrust are group purchasing organizations for hospitals.

The six companies did not immediately respond to Reuters requests for comments.