WASHINGTON?- President Barack Obama is poised to unveil executive action that will shield possibly around 5 million immigrants living in the US illegally from deportation, according to advocates in touch with the White House, an order that would set up a confrontation with Republican leaders.

Republicans have warned the president that such unilateral White House action would deeply complicate prospects of Congress passing legislation to overhaul the immigration system. Obama, under pressure from Latino advocates to act, argues executive action is necessary because the Republican-led House never acted on a bipartisan immigration bill passed last year by the Senate.

Timing of Obama's announcement is unclear, though it's expected before the end of the year. White House Press Secretary Josh Earnest said Obama would review final recommendations after returning from his Asia trip next week.

The estimate of 5 million includes extending deportation protections to parents and spouses of US citizens and permanent residents who have been in the country for some years. The president is also likely to expand his 2-year-old program that protects young immigrants from deportation.

Republicans, who are poised to take control of both chambers of Congress following last week's midterm elections, vowed to oppose Obama's plans.

"We're going to fight the president tooth and nail if he continues down this path. This is the wrong way to govern. This is exactly what the American people said on Election Day they didn't want," House Speaker John Boehner, a Republican, said Thursday. "And so, all the options are on the table."

Some conservatives in the House and Senate announced plans to push for language in must-pass spending bills to block the president from acting. But other Republicans warned that such a push could result in another government shutdown like the one last year over Obama's health care plan.

The advocates, who spoke on condition of anonymity ahead of a public announcement, said that final details of the plan remained in flux. But the White House is likely to include parents and spouses of US citizens and permanent residents, stipulating that they've resided in the US for some period of time?- possibly as little as five years. That group totals around 3.8 million people, according to the Migration Policy Institute.

Although Obama is not able to grant citizenship or permanent resident green cards on his own without Congress, he can offer temporary protection from deportation along with work authorization, as he has done in the past.

Adjustments also are expected to the existing Deferred Action for Childhood Arrivals program that allowed immigrants under 31 who had arrived before June 2007 to apply for a reprieve from deportation and a work permit. More than 600,000 young immigrants have been shielded from deportation to date under the program. Removing the upper age limit so that applicants don't have to be under 31?- one option under consideration?- would make an additional 200,000 people eligible.