United States President Barack Obama will defiantly bypass Congress and unveil executive actions Thursday to relax immigration policy and shield as many as 5 million people from deportation.

Claiming Washington has allowed the immigration issue "to fester for too long," Obama will announce the new measures during a prime time address Thursday evening (01:00 Friday UTC) and then sign the executive actions at a rally in Las Vegas, Nevada the following day.

Up to 5 million people currently in the United States illegally are expected to be protected from deportation and made eligible for work permits under the plan. Deportation protection would extend to the parents and spouses of US citizens and permanent residents who have been in the United States for several years.

Obama is also expected to expand a program called Deferred Action for Childhood Arrivals (DACA) which shields young immigrants from deportation. Immigrants protected from deportation would not be entitled to federal health or tax benefits under the plan, according to administration officials.

The immigration order is also expected to include a border security element and easier access to visas for high-skilled foreign workers.

Obama claims he has waited long enough for Congress to reform US immigration laws, as a majority of Republicans have repeatedly thwarted efforts to overhaul the system.

"Everyone agrees that our immigration system is broken," Obama said. The goal is to "make the system work better even as I continue to work with Congress and encourage them to get a bipartisan comprehensive bill that can solve the entire problem."

Looming showdown

Congressional Republicans -who won majorities in both houses in recent elections - are vehemently opposed to Obama's proposed unilateral immigration action, decrying such a move as "amnesty," and claiming it will poison any chance for bipartisan cooperation.

"If 'Emperor Obama' ignores the American people and announces an amnesty plan that he himself has said over and over again exceeds his constitutional authority, he will cement his legacy of lawlessness and ruin the chances for congressional action on this issue and many others," said Michael Steel, spokesman for House Speaker John Boehner.

Representative Paul Ryan, the leading Republican voice on fiscal policy and a possible 2016 presidential candidate, called Obama's planned move, "a partisan bomb."

"Under the Constitution, no president can go it alone without consequences," number two Senate Republican John Cornyn said.

But Republicans are divided on how best to respond to Obama's long-awaited action.

Some conservatives, such as Alabama Senator Jeff Sessions, have advocated fighting any potential immigration executive order by imposing funding restrictions in must-pass spending bills - a move that could potentially lead to a government shutdown.

South Carolina Senator Lindsay Graham, an architect of a landmark immigration bill that passed the Senate but died in the House, urged caution.

"You can't capitulate, but you need to push back smartly," he said. "If you overreact, then it becomes about us and not about President Obama."

Immigration decree a sharp reversal

As Obama prepares to unveil his executive orders, he has drawn criticism for apparently contradicting his own prior statements on executive authority as regards immigration policy.

"The problem is, is that I'm the president of the United States. I'm not the emperor of the United States. My job is to execute laws that are passed," Obama declared in February 2013, responding to a young activist who begged him to halt deportations that were separating families.

And in September of last year, Obama told Spanish language broadcaster Telemundo, that he could not act alone to broaden the deportation protection he enacted for young immigrants brought illegally to the US as children.

"if we start broadening that, then essentially I would be ignoring the law in a way that I think would be very difficult to defend legally. So that's not an option," Obama said.

Majority opposed to executive overhaul

Public opinion polling found more Americans opposed to an executive order to overhaul immigration than in favor. A joint poll by NBC News and the Wall Street Journal found 48 percent would prefer Obama not to act unilaterally to overhaul the immigration system, while 38 percent supported such a move. 14 percent had no opinion or were unsure.

bw/jm (AP, AFP, Reuters, dpa)