Health care coverage for newly legalized immigrants is emerging as a thorny issue in Congress’ drive to remake the nation’s immigration system, posing hard-to-solve problems for Senate negotiators and threatening a bill-writing effort in the House.

The question is how much access to taxpayer-subsidized care should be granted to immigrants who were here illegally and are embarking on a path to citizenship. Answering it has pulled the noxious politics around President Barack Obama’s signature health care law into the immigration debate.

That’s threatening fragile alliances between Republicans and Democrats, already causing one key House member, GOP Rep. Raul Labrador of Idaho, to ditch a bipartisan group in the House that has been struggling to finalize a comprehensive immigration bill.

“What may be the story at the end of this session is that Obamacare killed immigration reform,” Labrador said before a last-gasp effort failed this week to resolve the health care dispute in a way he could accept. Now the seven other members of the House group are moving forward without Labrador, who said their proposal doesn’t go far enough to ensure that immigrants must pay for all their own health care costs without leaving taxpayers on the hook for any of it.

Health care and immigrants was a hot-button issue even before Republican Rep. Joe Wilson of South Carolina yelled “You lie!” at Obama four years ago as the president told Congress that immigrants in the country illegally wouldn’t be covered under his health plan. For Republicans, allowing immigrants here illegally to get coverage under Obamacare remains a nonstarter, even once they’ve taken the first steps toward legalizing their status.

“We cannot be providing Obamacare subsidies to people who have been violating our immigration laws,” said Sen. Marco Rubio, R-Fla., an author of a bipartisan immigration bill that the full Senate began debating Friday.

The Senate bill bars immigrants in a new provisional legal status, the first step toward a green card and citizenship, from getting taxpayer-subsidized care. That includes Medicaid and tax subsidies to buy coverage in the new state purchasing exchanges being set up by Obamacare. The immigrants would be in provisional status for 10 years, and only once they get a permanent resident green card would they be able to access Obamacare subsidies.

The approach is opposed by immigrant advocates who pushed for provisional legal immigrants to be allowed government-subsidized care, arguing that it makes sense for public health and the economy. But the idea was opposed by Republicans, and even Democratic authors of the Senate bill didn’t fight too hard for it, advocates said, partly because it would have greatly increased the cost of the legislation. By just how much is unclear. But the Obamacare tax subsidies will cost on average about $5,300 annually for each person who gets them starting next year, according to the Congressional Budget Office.

“We definitely were pushing from the start, and basically we tried to remind the Democrats that this was sort of an unfulfilled promise from the Affordable Care Act, when undocumented immigrants were excluded,” said Sonal Ambegaokar, health policy attorney at the National Immigration Law Center. She said some Democrats were open to the arguments but that it quickly became clear they wouldn’t prevail, “for political reasons, and not economic reasons.”

As the House immigration group moves forward trying to unveil a bill, it may include placeholder language on health coverage similar to what’s in the Senate measure.

So where does that leave newly legalized immigrants in provisional status with no access to publicly funded care?

In the aftermath of Wilson’s outburst, the White House tightened its stance on the Affordable Care Act, saying that immigrants here illegally wouldn’t be able to buy coverage in new health care exchanges even using their own money. But the Senate immigration bill does allow them to go into the exchanges with their own money once they obtain provisional legal status. For most, that would be prohibitively expensive.

Although current law bars immigrants here illegally from Medicaid and Obamacare, pregnant women, children, seniors and the disabled have access to emergency Medicaid services. Immigrants here illegally can also access community health centers. That would be the case for immigrants getting provisional status under the immigration bill, too.

Beyond that, a certain number of immigrants would get employer-sponsored care. Right now, about 30 percent of immigrants here illegally are covered that way, according to the Migration Policy Institute. That number would likely rise at least somewhat if the immigration bill becomes law.