(Bloomberg) Almost a third of 32 hospitals and health systems involved in an experiment aimed at changing the way medical providers are paid may exit the program, a potential threat to the Affordable Care Act’s ambitious cost-saving goals.

Medicare’s “Pioneer” program is designed to save money by more efficiently managing care for patients with chronic diseases, such as diabetes and dementia. The providers agreed to a three-year plan to forgo traditional fee-for-service payments, where hospitals charge for every procedure, and instead get a fixed monthly stipend for individual patients.

Begun in January 2012, Pioneer is one of several programs involving 252 providers created under the law to experiment with new payment models. Nine Pioneer members have told the U.S. they may exit, said Brian Cook, a Centers for Medicare and Medicaid Services spokesman. At least four may join other accountable-care programs that carry less financial risk, he said.

Note: Read our discussion guidelines before commenting.