A 25-year-old federal drug discount program has grown so big and controversial that it faces a fight for survival as federal officials and lawmakers furiously debate the program's reach.

The program, known as 340B, requires pharmaceutical companies to give steep discounts to hospitals and clinics that serve high volumes of low-income patients.

The Centers for Medicare & Medicaid Services struck a blow to the program this month announcing a final rule to cut Medicare payments for hospitals enrolled in the program by 28 percent, or about $1.6 billion. The American Hospital Association, the Association of American Medical Colleges, America's Essential Hospitals and others filed suit on Nov. 13, arguing that the agency lacks the authority to slash the payments and that the rule undermines the intent Congress had when creating the program.