Republicans vow to fight 'illegal' Obama immigration plan
House Speaker John Boehner (R-OH) speaks during a press conference at the House Republican Issues Conference in Cambridge, Maryland, Jan. 30, 2014 (AFP)

Republican reaction was swift and savage Thursday to President Barack Obama's unilateral plan to bring millions of undocumented non-citizens out of the shadows and make them eligible for work permits.

"That's just not how our democracy works," House Speaker John Boehner said in a statement released minutes after the White House unveiled details of Obama's plan, which lifts the threat of deportation for up to five million people living in the shadows.

"The president has said before that 'he's not king' and he's 'not an emperor,' but he's sure acting like one."

Republicans, many of whom hammer as "amnesty" any plan to legalize non-citizens who broke the law to get to the United States, have spent weeks considering ways they might be able to block Obama's executive order.

"I will try to defund the effort for him to go it alone," warned Senator Lindsey Graham, a Republican who helped craft landmark immigration reform legislation last year that passed the Senate but failed in the Republican-run House of Representatives.

"We will challenge him in court."

Senator Rand Paul, a favorite of the Tea Party movement that widely opposes Obama's immigration action, called on the House to pass a resolution condemning the plan as illegal, a move that could pave the way for a court challenge.

Congress must soon debate and pass spending legislation that funds government in 2015, and conservatives are eyeing the must-pass bills as potential leverage against the immigration order.

Several have argued for defunding the federal agencies responsible for issuing temporary work permits.

But the House Appropriations Committee, which oversees the budget process, indicated that such action would be impossible, because the main agency tasked with implementing Obama's plan is self-funded through immigration application fees and not through the budget approved by Congress.

While most Democrats are thought to support the president, he received criticism from his own ranks.

"Congress must work with the president to debate the issues and vote to secure our borders, create a tough legalization process, and ensure employers don't hire illegal immigrants," Senator Joe Manchin said.

Manchin opposed Obama's unilateral step, but said he also disagreed with the House's decision not to vote on the bipartisan reform bill that passed the Senate in June 2013.