(Reuters) -Shares of health insurers fell about 2% to 10% in early trading on Monday after the U.S. Senate struck a deal to end the 40-day federal shutdown without extending Affordable Care Act subsidies, setting up a December vote on the issue instead.

Disagreement over extending the subsidies, which are due to expire at the end of the year, has been at the heart of the longest-ever federal shutdown that has sidelined federal workers, delayed food aid and snarled air travel.

As part of the deal, which the Senate agreed to on Sunday, Republicans and a small group of Democrats agreed to a December vote on extending the subsidies, which have been in place since the COVID-19 pandemic and are due to expire at the end of 2025.

Without them, most of the 24 million people enrolled in these plans will see a sharp increase in their health insurance costs for 2026.

Shares of Centene slid 9.8%, Molina Healthcare slipped 4.9%, Elevance Health was down 2% in early trading.

"While it looks like a vote will occur on the issue in December, it leaves uncertainty around this issue. If ACA subsidies aren't extended, that's a negative for health insurers and hospitals," said James Harlow, senior vice president at Novare Capital Management.

Low-income Americans enrolled in the plans, created by President Barack Obama, receive government subsidies based on their income. The subsidies have enabled enrollment to double to 24 million since they were put in place in 2021.

Meanwhile, President Donald Trump on Sunday reiterated a call to end the subsidies, posting on his Truth Social platform that they were a "windfall for Health Insurance Companies, and a DISASTER for the American people".

The Trump administration tried and failed to repeal the law, also known as Obamacare, during his first term.

He called for the government funds to be sent directly to individuals to buy coverage on their own. "I stand ready to work with both Parties to solve this problem once the Government is open," Trump said in the post.

Trump's comments also infuse more uncertainty for insurers, Harlow said.