MIAMI — In the weeks since the Supreme Court ruled that states could opt out of a plan to vastly expand Medicaid under President Obama’s health care law, several Republican governors have vowed to do just that, attacking the expansion as a budget-busting federal power grab.

But it may not be so easy. A battle is brewing here in Florida, where Gov. Rick Scott took to national television soon after the ruling to announce that he would reject the expansion. Advocates for the poor and some players in the health care industry — especially hospitals, a powerful political lobby — intend to push back.

Hospital associations around the country have already signed off on cuts to reimbursement rates under the health care law on the assumption that the new paying customers they would gain, partly through the Medicaid expansion, would more than cover their losses.

“If we’re going to walk away from that coverage, we’ll simply see those dollars we contributed through cuts in hospital payments go to covering people in other states,” said Bruce Rueben, president of the Florida Hospital Association. “It’s a bad deal for people in Florida if it plays out that way.”