The Senate is set to vote Thursday on two competing proposals to avert a steep rise in health care costs for tens of millions of Americans who rely on enhanced Affordable Care Act tax credits—benefits that will expire at the end of the year without congressional action.

Both measures, one drafted by Democrats and the other by Republicans, are widely expected to fail. Their collapse would leave lawmakers with only days to find a solution before the enhanced subsidies expire on Jan. 1, triggering major premium increases for many households. So far, there is little sign of a bipartisan breakthrough.

The Democratic plan slated for a vote would extend the enhanced ACA subsidies for three years. These expanded tax credits, first enacted during the COVID-19 pandemic, significantly lowered monthly insurance costs for millions of enrollees.

On Wednesday, Senate Minority Leader Chuck Schumer urged colleagues to support the measure, calling it the “only realistic path left” to prevent premiums from “doubling or tripling” in the new year.

“We have 21 days until Jan. 1,” Schumer said on the Senate floor. “After that, people’s health care bills will start going through the roof. There is only one way to avoid all of this—a clean, direct extension of this urgent tax credit.”

The vote is part of an agreement brokered by a group of Senate moderates to end the recent 43-day government shutdown, which was triggered in large part by the dispute over the soon-to-expire ACA subsidies.

However, with Democrats in the minority, the proposal would need at least 60 votes to pass—an unlikely outcome. Senate Majority Leader John Thune made clear Wednesday that Republicans will not support the Democratic bill.

With neither party’s plan expected to clear the chamber, Congress is barreling toward a year-end deadline with no consensus in sight and millions facing potentially dramatic increases in their health insurance premiums.