A Republican congressman from a heavily Hispanic district is breaking ranks from his party to join Democrats in an eleventh-hour push for a broad immigration overhaul before the end of the year.

Rep. Jeff Denham (R-Calif.) plans to sign on as the lone GOP member with 185 Democrats to co-sponsor a plan that would give millions of unauthorized immigrants the chance to attain citizenship.

A handful of House Republicans have expressed support for citizenship legislation similar to the bipartisan bill that passed the Senate over the summer. But Denham is taking the additional — and politically provocative — step of locking arms with House Minority Leader Nancy Pelosi (Calif.) and other Democrats trying to neutralize opposition from House conservatives and shake up a polarized immigration debate.

“I’m the first Republican,” he said in an interview. “I expect more to come on board.”

With fewer than 20 working days left in the current session and Congress focused largely on high-stakes budget negotiations, some House Republicans have argued in recent days that they won’t have time to debate immigration this year. Asked in a Bloomberg TV interview over the weekend if a broad immigration overhaul stood a chance of passing in the coming weeks, Rep. Tom Cole (R-Okla.) said flatly, “No.”

Denham’s announcement comes as Democrats and immigrant advocates are trying to force House Speaker John A. Boehner’s (R-Ohio) hand on the issue. Key to their strategy is a new compromise bill designed to lure away enough centrist GOP members that the speaker would feel compelled to allow a vote of the full chamber — just as he did to end the government shutdown and avoid a financial default.

If Boehner were to refuse to allow a vote, Democrats say they could blame him and Republicans for blocking a “bipartisan” bill on the campaign trail next year .

The measure adopts most of the bipartisan Senate legislation, but it adds in a House GOP-backed border security bill written by Rep. Michael McCaul (R-Tex.) that won unanimous, bipartisan approval last May in the House Homeland Security Committee.

That language, which would direct the government to achieve a 90 percent apprehension rate of illegal border crossers, would replace controversial language added to the Senate bill at the last minute that would add 700 hundred of miles of fence and 20,000 agents along the U.S.-Mexico border.

“We put forward a bill that we figured Republicans could sign onto,” said Rep. Joe Garcia (D-Fla.), a chief sponsor of the new House legislation.

Garcia said Boehner and the GOP House leadership now face a decision on whether to once again allow the full chamber to vote on a bill that could pass with a majority of Democrats and a minority of Republicans.

“There is a way forward,” Garcia said. Previewing the line of attack that awaits Republicans if nothing happens, Garcia added: “The Democrats have put it up. The Republicans have decided to kill immigration reform.”

Ali Noorani, head of the National Immigration Forum, described Denham’s announcement as a major development. He said the new House bill was a “good-faith effort by the Democrats and not a political grenade.” But, Noorani added, advocates remain far from attracting the support they need to make the measure more than merely symbolic.

“We need votes,” Noorani said. “Until it gets to that magic 218 number, it’s a message bill.”

Immigration advocates are hoping to add further pressure on House conservatives in the coming days by bringing as many as 600 pastors, business owners and law enforcement officials representing dozens of key congressional districts to Capitol Hill for lobbying meetings.

Advocates are circulating a list of 28 target House Republicans who have expressed support in the past for an immigration overhaul, some of whose districts include a large number of Hispanic voters.

Like many Republicans, Boehner and other House leaders voiced support for immigration legislation in the wake of the 2012 presidential election in which Hispanic voters overwhelmingly rejected the GOP. Growing concerns about the party’s future viability with Hispanics spurred Senate Republicans to the negotiating table to craft a broad citizenship bill.

But House conservatives, many of whom represent districts with few Hispanic voters, have been reluctant — instead backing a series of smaller measures, to boost border security or add foreign worker visas for high-tech firms and the agriculture industry.

A spokesman for Boehner, Brendan Buck, last week underscored the speaker’s support for changing the immigration system with a “deliberate approach.”

“The House will not consider any massive, Obamacare-style legislation that no one understands,” Buck said. “Instead, the House is committed to a common sense, step-by-step approach that gives Americans confidence that reform is done the right way.”

The issue has spurred emotional internal debates among House Republicans about whether to support a citizenship plan or perhaps some sort of legalization for the 11 million unauthorized immigrants in the country that would stop short of citizenship.

Hispanic population growth in some Republican districts has led some in the House GOP caucus to argue in favor of citizenship. Business groups have also urged support.

Denham faces a Democratic challenge next year. His district, which covers a heavily agricultural area of California’s central valley, is competitive, with a population that is more than 40 percent Hispanic. Sonia, his wife of 20 years, is Hispanic. Denham said he learned Spanish to communicate with her family, including to help his Mexican father-in-law through the process of gaining U.S. citizenship.

He and his family “have been talking about immigration for over a decade now,” he said.

The congressman is announcing his sponsorship of the immigration bill in an interview on the Spanish-language channel Univision’s popular “Al Punto” program, set to air Sunday. Denham spoke in Spanish with anchor Jorge Ramos for much of the conversation, which was taped late last week.

Denham, in an interview with The Washington Post, said he agreed to sign onto the Democrats’ legislation after they agreed to include a provision that would put certain young unauthorized immigrants who serve in the military on a path to citizenship.

Denham said the military measure and the border provisions should address most concerns that have been expressed by his GOP colleagues. The bill, he said, is “far different than anything we’ve seen in the past.”

As for whether his party leadership would let votes happen on any immigration proposals, Denham said he expects the House will get the chance to address the issue in some fashion. “They’ve told me that we’re going to have this [issue] on the floor by the end of the year.”