(Bloomberg) -- Health systems in at least 14 states are joining a new version of a program under Obamacare meant to lower costs in the half-trillion-dollar Medicare program, after some groups quit an earlier effort.

It’s the latest initiative to change the way hospitals and doctors are paid under the Patient Protection and Affordable Care Act, which became law in 2010 as President Barack Obama’s signature domestic policy achievement.

In all, 21 systems are taking part in the Next Generation Accountable Care Organization program, which started on Jan. 1, the Centers for Medicare and Medicaid Services said Monday. The systems, such as Steward Health Care and WakeMed, will cover about 650,000 individuals this year.