Sen. Marco Rubio (R-Fla.) speaks at the Faith and Freedom Coalition Road to Majority Conference in Washington on Thursday. (Charles Dharapak/AP)

After spending years unsuccessfully trying to overturn “Obamacare,” Republicans are now attempting to use President Obama’s landmark health-care law to derail his top second-term initiative — a sweeping overhaul of the nation’s immigration system.

Conservatives in both chambers of Congress are insisting on measures that would expand the denial of public health benefits to the nation’s 11 million illegal immigrants beyond limits set in a comprehensive bill pending in the Senate.

In the House, Republicans are considering proposals that would deny publicly subsidized emergency care to illegal immigrants and force them to purchase private health insurance plans, without access to federal subsidies, as a requirement for earning permanent legal residency.

In the Senate, Marco Rubio (R-Fla.) has endorsed an amendment to a comprehensive immigration bill he helped negotiate that would deny health benefits to immigrants for five years after they become legal residents — two years after they would be eligible to become citizens under the legislation.

Some Republicans, eager to capi­tal­ize on public uncertainty about the complexities of the Affordable Care Act, are casting the immigration legislation as a similarly unwieldy law.

The immigration bill “reminds me of a more recent piece of legislation: Obamacare,” Sen. Mike Lee (R-Utah) said on the Senate floor last week. “It grants broad new powers to the same executive branch that today is mired in scandal for incompetence and abuse of power. Total cost estimates are in the trillions. And rather than fix our current immigration problems, the bill makes many of them worse.”

The insertion of the politics of health-care reform — one of the most polarizing issues in Washington — into the immigration debate threatens to split open the emerging bipartisan coalitions that are crucial to passing a bill.

This month, Rep. Raúl R. Labrador (R-Idaho) blamed a standoff over health-care benefits for his decision to drop out of bipartisan talks with seven colleagues who were negotiating a House alternative to the Senate immigration proposal. That has forced House leaders to proceed with a series of smaller-scale proposals next week in lieu of a sweeping agreement.

“When I joined the group, I was told that the aliens would have to pay for their own health care,” Labrador told Fox News. “Now that has changed. And I can’t agree to all of the exceptions.”

Frustrated Democrats argue that Republicans are picking a fight where one does not exist. In both chambers, Democrats say, they have agreed that illegal immigrants would not be eligible for public benefits — including health-care subsidies and Medicaid — as they embark on a path to permanent legal status, which would take at least 10 years under the Senate plan.

“We have said since Day One . . . that undocumented people will not have access to subsidies in the Affordable Care Act,” House Minority Leader Nancy Pelosi (D-Calif.) said last month. “Any thought that we want to do something different than that is simply not true. It is a bottom line. No need to even discuss it.”

Under current law, illegal immigrants and legal residents of fewer than five years are mostly barred from receiving benefits under Medicaid, the joint state-federal health insurance program for the poor. That restriction does not apply to poor immigrants who show up at hospital emergency rooms, however.

While writing the Affordable Care Act, Congress sidestepped the dicey issue of illegal immigration by excluding immigrants who are in the country illegally from its provisions. That means that those immigrants will not get government subsidies to help them buy private insurance plans, nor can they benefit from the law’s expansion of Medicaid.

At the same time, however, they are exempted from the mandate, taking effect next year, that every person must carry health insurance or face a tax penalty.

Some Republicans think it would be unfair to exclude such immigrants from the insurance mandate. One proposal championed by Labrador, according to people familiar with the private House negotiations, would require illegal immigrants to purchase their own insurance, without access to federal health exchanges, as a prerequisite for citizenship.

Democrats argue that making the immigrants subject to the mandate could impose an insurmountable burden on them because of potentially hefty premiums that would not be offset by federal subsidies available to others. That burden could also discourage people from coming out of the shadows to apply for legal status, said Priscilla Huang, policy director for the nonpartisan Asian and Pacific Islander American Health Forum.

“If we want them to become citizens and fully integrated into their communities and our country, we should really treat them as such,” Huang said.

Aides said Labrador simply wanted to include language in the House bill that would ensure that illegal immigrants were responsible for paying for their own care.

Other members of the immigration working group resisted out of fear that the language Labrador proposed would have meant that illegal immigrants with unpaid medical bills would not be eligible for permanent legal residency and could be deported, according to Democratic aides.

Jennifer Ng’andu, the director of health policy for the National Council of La Raza, said the true motive for some Republicans is unrelated to immigration reform. Rather, she said, it is to perpetuate “ideological warfare” against the Obama health-care law.

In 2009, Rep. Joe Wilson (R-S.C.) shouted “You lie!” after Obama said, during his State of the Union address, that immigrants in the country illegally would not be eligible for federal health-care subsidies. Since the Affordable Care Act was narrowly approved a year later, the House GOP has voted to repeal it more than 30 times, symbolic gestures that had no chance of consideration in the Democratic-controlled Senate.

As the Obama administration has moved to sign up uninsured Americans by the October deadline, Republicans have sought to paint a picture of widespread confusion and chaos.

In a video message to constituents Friday, Rubio said that “Obamacare is bad for America” and that the health-care program “can never and will never work and may even contribute to bankrupting our country.”

Last week, Rubio announced he would co-sponsor an amendment with Sen. Orrin G. Hatch (R-Utah) to mandate that illegal immigrants cannot get access to public benefits until five years after they earn green cards signifying permanent legal status.

That would mean that, although such immigrants could be eligible for citizenship after 13 years, they would not be allowed to access the health subsidies for at least 15 years.

“The 13-year-long pathway to citizenship will be hard enough,” said Sen. Mazie Hirono (D-Hawaii). “The restrictions on federal safety-net programs make the pathway even more treacherous.”