One reason is that the law changed the payment rates for just about every type of health care professional who treats Medicare patients. Every time Medicare sets a payment rate, it needs to cite a legal authority. And for the past two years, says Rosenbaum, that legal authority has been the Affordable Care Act.

So if the law is found unconstitutional, she says, every one of those changes “doesn’t exist anymore because the law doesn’t exist.”

And the result? “You have agencies sitting on two years of policies that are up in smoke,” she says. “Hospitals might not get paid. Nursing homes might not get paid. Doctors might not get paid. Changes in coverage that have begun to take effect for the elderly, closing the doughnut hole might not happen. We don’t know.”

And many of those facilities serve not just Medicare patients but the rest of the population, too. Hence, the spillover could affect the health care system as a whole.