State leaders and healthcare advocates are warning that insurance premiums will spike in January for about 400,000 Massachusetts residents if Congress doesn’t extend Affordable Care Act tax subsidies that are about to expire.

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The U.S. Senate is expected to vote Thursday on a Democratic proposal to extend the subsidies, and Massachusetts Gov. Maura Healey said she’s calling on President Trump and Republicans in Congress support that extension.

“Because if they don’t, people are going to suffer,” Healey said at a press briefing on Tuesday. “People are going to go without care. It’s totally unaffordable, it’s totally unacceptable, and it just doesn’t need to be.”

The biggest impact will be on about 26,000 residents making just over 400% of the federal poverty level, which is just over $60,000 a year for an individual, said Alex Sheff of the group Healthcare For All. Those people, Sheff said, are set to lose the tax credits altogether.

“So they’re going to now just have to pay the market rate for that insurance,” Sheff said. “We’re hearing from folks that are going to see their premiums double, even triple, for the same level of coverage.”

Audrey Morse Gasteier, executive director of the Massachusetts Health Connector, is scheduled to testify about the issue Wednesday before a Senate panel in Washington, D.C.

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“I will be sharing details on what we at the Health Connector are seeing and hearing right here on the ground in Massachusetts, as the harms of inaction bear down on hundreds of thousands of residents,” Morse Gasteier said at Tuesday’s press conference. “For the people we serve who depend on enhanced premium tax credits, this issue is not a remote political debate. It is a gut punch to those trying to make ends meet and trying to maintain their health and their financial security. We do not have to go backwards like this.”

The subsidy situation is creating uncertainty as Massachusetts residents face a Dec. 23 deadline to enroll in Health Connector plans for 2026.

“While we do everything we can to give Massachusetts residents clear information about changes resulting from federal policy and options to stay covered, we continue to implore policymakers in Washington to do the right thing and extend the enhanced premium tax credits,” Morse Gasteier said.