(NewsNation) — Congress has less than a month to vote on extending subsidies tied to the Affordable Care Act.

Democrats who held out during the government shutdown for a vote on the subsidies — which help mitigate the cost of private health insurance — have warned that millions may not be able to pay for health insurance if those tax credits expire on Dec. 31.

Premiums could more than double next year for 24 million Americans, according to a preview of the available plans released by the Trump administration.

Nearly half of American adults, 47%, are worried they won’t be able to afford necessary health care, according to a West Health-Gallup poll from November. Participants reported the highest level of concern around health care in the last four years.

In the last three months, 1 in 5 said they or someone in their family couldn’t pay for their prescription medications — another record high.

Joel White, president of the Council for Affordable Health Coverage, told NewsNation that ever-increasing medical costs are not sustainable in the long run.

“If current trends persist, by 2032 the typical American family will pay 40% … of their income just on health care premiums,” White said.

“The subsidies are a temporary fix. We’ve got a very expensive system. Subsidizing an expensive system will get you a more expensive system,” he added.

President Donald Trump told members of Congress not to “waste time and energy” on an extension, despite recently saying he knows one might be necessary, according to NewsNation partner The Hill.

Sen. Amy Klobuchar, D-Minn., said the Senate will vote on the subsidies before the end of the month, though House Democrats have not shared that confidence.

“That vote will happen. And whether it will pass is in the hands of Donald Trump and the Republicans,” Klobuchar told CNN.

NewsNation’s Anna Kutz contributed to this report.