Federal officials have reportedly confirmed that they are cutting off a major portion of funding for New York’s Essential Plan, opening a roughly $1 billion hole in the state budget and raising new doubts about the future of a rapidly growing health insurance option for the working poor.

The lost money—about a quarter of the Essential Plan’s budget—has been in jeopardy for months. Its demise seemed all but guaranteed in October, when President Trump followed through on a threat to halt payments under Obamacare’s cost-sharing reduction program, which a court had ruled to be unconstitutional and which was the source of more than $900 million a year in Essential Plan funding.

Until now, however, the Cuomo administration had held out hope that the Essential Plan’s funding might be exempted from Trump’s order—hope that was recently dashed when the federal Centers for Medicare & Medicaid Services notified Albany that a quarterly payment due this month would not be forthcoming, as reported by Politico.

There’s also a chance that Congress will revive cost-sharing reductions—as the Senate leadership agreed to do in a deal to secure votes for its tax overhaul plan. It’s not clear, however, that the House would follow suit.

The Essential Plan, also known as a “basic health plan,” is an optional benefit under the Affordable Care Act that was exercised by only two states, New York and Minnesota. New York’s version is available to people earning up to 200 percent of the federal poverty level—$24,120 a year for an individual, $49,200 for a family of four—and costs either $0 or $20 per month, depending on income.

To finance the program, the state is entitled to 95 percent of the federal subsidies that Essential Plan enrollees would have received if they had bought private insurance through the Obamacare exchange. For New York, that has amounted to about $4 billion a year – three-quarters of which reflected what enrollees would have received in premium tax credits, and $1 billion a year that insurance companies would have collected in cost-sharing reductions, to offset the reduced copayments and deductibles they are required to provide to low-income customers.

In response to a lawsuit by the House GOP, however, a federal court ruled in May 2016 that funding for the cost-sharing reductions was never properly appropriated by Congress. President Obama continued the payments while the case was being appealed, but Trump stopped them in October.

Neither the lawsuit against cost-sharing reduction nor the court’s ruling specifically mentioned funding for the Basic Health Plans in New York and Minnesota, leaving some doubt as to its fate. House GOP lawyers even declared in a legal brief that their case would not affect funding for the state-run plans. However, their brief did not identify a valid appropriation that would cover cost-sharing reduction payments to states but not insurers.

Despite the uncertainty, the Cuomo administration has continued encouraging people to sign up for the Essential Plan. It reported on Thursday that enrollment had reached 710,000, up 27,000 in just the past two months.

Barring a reprieve from Congress, the state faces a choice between disenrolling hundreds of thousands of New Yorkers, or backfilling with $1 billion of its own money. Cancelling the program would come with costs of its own: Some 250,00 Essential Plan members are legally present immigrants at or below the poverty line who are entitled to health coverage under state court rulings.

By shifting those immigrants from Medicaid (where the state paid 100 percent of the cost) into the Essential Plan (which is mostly federally funded), the state has realized a net savings of about $850 million—a savings that would be lost if the Essential Plan ended.