Health insurers warn that a move by the Trump administration on Saturday to temporarily suspend a program that was set to pay out $10.4 billion to insurers for covering high-risk individuals last year could drive up premium costs and create marketplace uncertainty.

The Affordable Care Act’s (ACA) “risk adjustment” program is intended to incentivize health insurers to cover individuals with pre-existing and chronic conditions by collecting money from insurers with relatively healthy enrollees to offset the costs of other insurers with sicker enrollees.

President Donald Trump’s administration has used its regulatory powers to undermine the ACA on multiple fronts after the Republican-controlled Congress last year failed to repeal and replace the law. About 20 million Americans have received health insurance coverage through the program.

The Centers for Medicare and Medicaid Services (CMS), which administers ACA programs, said on Saturday that months-old conflicting court rulings related to the risk adjustment formula prevent them from making payments.

CMS was referring to a February ruling from a federal court in New Mexico that invalidated the risk adjustment formula, and a January ruling from a federal court in Massachusetts that upheld it.

America’s Health Insurance Plans (AHIP), a trade group representing insurers offering plans via employers, through government programs and in the individual marketplace, said the CMS suspension would create a “new market disruption” at a “critical time” when insurers are setting premiums for next year.

“It will create more market uncertainty and increase premiums for many health plans — putting a heavier burden on small businesses and consumers, and reducing coverage options. And costs for taxpayers will rise as the federal government spends more on premium subsidies,” AHIP said in a statement.

CMS administrator Seema Verma said in a statement the administration was “disappointed” in the February ruling and that CMS has asked the court to reconsider and “hopes for a prompt resolution that allows CMS to prevent more adverse impacts on Americans.”

But supporters of the ACA criticized the CMS announcement as the latest move by the Trump administration to undermine former President Barack Obama’s healthcare law, also known as Obamacare.

“We urge the Trump administration to back off of this dangerous and destabilizing plan, and instead begin working on bipartisan solutions to make coverage more affordable,” said Brad Woodhouse, the executive director of Protect Our Care, a progressive group that supports Obamacare.