The Obama administration is warning the U.S. Supreme Court that striking down the health care law could have major consequences for Medicare.
Medicare handles 100 million monthly claims. The administration contends there would be "extraordinary disruption" in the system if it is forced to unwind transactions based on changes required by the Affordable Care Act.
Some opponents have accused the president of trying to intimidate the courts.
Last month, on two separate occasions, President Obama publicly cautioned the Supreme Court against overturning his law, saying that would amount to judicial activism.
He also said it would be unprecedented for the justices to strike a law passed by a democratically elected Congress
But during the case, Justice Anthony Kennedy had said it would be more a case of judicial activism if the justices picked through the law piece by piece, only keeping certain parts of it.
"That, it seems to me, can be argued at least to be a more extreme exercise of judicial power than striking the whole," Kennedy said.
Last year, the Justice Department told a lower court that reversing the Medicare payment changes would "impose staggering administrative burdens," and "could cause major delays and errors" in payment.
The ranking Democrat on the House Ways and Means Committee is taking up the administration's argument.
"There is no doubt that striking down (the) Medicare provisions would be enormously disruptive for patients, physicians, hospitals and countless other providers and suppliers," Rep. Sander Levin, D-Mich., said.
But former Medicare administrators disagree on the potential for major disruptions.
"There is an independent legal basis to pay providers if the Supreme Court strikes down the entire law," said Thomas Barker, former Health and Human Services general counsel for the George W. Bush administration.
Tom Scully, Medicare chief during former President Bush's first term, also does not foresee major problems, although he acknowledges it would be a "nightmare" for agency bureaucrats.
"It is highly unlikely in the short term that any health plan or provider would suffer," Scully said. "They're probably likely to get paid more going forward. If you look at the way the law was (financed), it was a combination of higher taxes and lower (Medicare) payments. That's what you would be rolling back."
Scully also dismissed the notion that one popular Medicare program would be jeopardized if the Supreme Court throws out the law.
"The idea that Medicare Advantage plans would shut down and patients would be thrown into the street is just people making up arguments to stir the pot," he said.
Administration officials say they are confident the entire law will be upheld by the Supreme Court and there is no planning to address what would happen if all or parts of it are struck down.
Sharp questioning by the court's conservative justices during public arguments has led many to speculate that at least parts of the law will be struck.