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US President Barack ObamaReuters

US President Barack Obama rolled out the most sweeping reforms in the country's immigration system on Thursday, bringing relief to 4.7 million undocumented immigrants by sparing them the threat of deportation.

However, Obama seems to have taken up the cudgel for immigrants at the cost of upsetting the resurgent Republicans in the process. He has openly dared the next Republican-majority Congress to challenge his reforms, following criticism from their quarters over his decision to bypass the Congress and take executive action.

"Scripture tells us that we shall not oppress a stranger, for we know the heart of a stranger -- we were strangers once, too. My fellow Americans, we are and always will be a nation of immigrants.," Obama said in his speech from the White House's East Room on Thursday, rolling out reforms not seen in a generation.

Terming America's immigration system as "broken", Obama said that welcoming immigrants "keeps us dynamic, entrepreneurial, and uniquely American".

He promised to make it easier and faster for high-skilled immigrants, graduates, and entrepreneurs to stay in the country.

Among the steps that Obama has planned in the immigration reforms are background checks on undocumented parents of US citizens who have been here for more than five years and to get them to pay taxes, and expanding work authorisation for high-skilled workers who are in line for a green card, among others as shared by the White House.

They will, however, not qualify for insurance under the healthcare law, another of Obama's much-contested reforms.

Thus, of the 11 million undocumented immigrants in the United States, Obama has brought temporary relief to at least 4.4 million through the reforms. He has also given hope to 270,000 people who will now be eligible for relief under the expansion of a 2012 move to stop deporting people brought illegally to the United States as children by their parents.

Obama pressed on the deportation of "felons, not families, criminals, not children, gang members, not a mom who's working hard to provide for her kids".

Obama also laid down a to-do list for the Congress: strengthen border security by adding 20,000 more Border patrol agents, cracking down on companies which hire undocumented immigrants, simplifying the legal immigration process, and giving a path to earned citizenship for undocumented immigrants who pass background checks and pay taxes.

However, Obama's exercising of powers of the Oval office did not go down too well with the Republicans, who recently won majority in the Congress.

"The president has said before that 'he's not king' and he's 'not an emperor,' but he sure is acting like one," House Speaker John Boehner said in a video, Reuters reported.

Obama, however, had a reply to the criticism. "To those members of Congress who question my authority to make our immigration system work better, or question the wisdom of me acting where Congress has failed, I have one answer: Pass a bill."