Several healthcare safety net groups sent a letter to congressional leaders Thursday asking them to put payments for insurance companies into a federal spending bill whose deadline is approaching next week.

The payments, called cost-sharing subsidies, help subsidize out-of-pocket medical expenses for low-income enrollees. They are estimated to reach $7 billion in 2017 and have become part of a legal and political battle that threatens their future. If insurers were to lose access to the funds, they would pull out of the Obamacare exchanges as quickly as they are able and would raise premiums.

"Issuers are currently determining their rates for 2018 and seek certainty as to whether the federal government will continue to fund CSRs," the safety net groups wrote in their letter. "The uncertainty posed … also can lead issuers to charge higher premiums for 2018 or even to exit the marketplace altogether."

Democrats have said that they want the funds to be appropriated in the continuing resolution due April 28, the spending bill safety net groups are advocating for.

The letter sent Thursday was written by America's Essential Hospitals, the Association for Community Affiliated Health Plans, the Association of Clinicians for the Underserved and the National Association of Community Health Centers.

The future of the cost-sharing reduction subsidies is in limbo because of a lawsuit filed by House Republicans when Barack Obama was president, which accused the administration of illegally distributing the payments. A federal judge sided with the House, and the Obama administration appealed the ruling.

Trump, who could drop the appeal, has said that he might withhold the funds as a way to bring Democrats to the negotiating table on legislation to gut Obamacare. The comment concerned insurers as well as healthcare providers, which could face an increase in the number of people unable to pay for their healthcare.

Health insurance, hospital and doctor groups sent a similar letter to the Trump administration and congressional leaders April 12.