President Obama will use his executive authority to allow up to five million undocumented immigrants to apply for relief from deportation, a major shift in immigration policy after years of stalled legislative efforts and promises of executive action.

Obama’s plan, laid out in a prime-time speech Thursday night, marks a significant moment in his presidency and entails the biggest changes to immigration policy since the 1980s. His decision to use an executive order came after Republicans in the House of Representatives failed to act on the issue over the past year and a half. 

“Scripture tells us that we should not oppress a stranger. For we know the heart of a stranger. We were strangers once, too,” Obama said Thursday night from the East Room of the White House. “My fellow Americans, we are and always will be a nation of immigrants. We were strangers once too. And whether our forebears were strangers who crossed the Atlantic or the Pacific or the Rio Grande, we are here only because that country welcomed them in.”

The president’s plan will be implemented this spring. It will affect less than half the estimated 11.3 million people living in the U.S. without legal status, and focus on keeping families together that might have been torn apart by deportations. Obama’s action will also go a long way to repairing his relationship with immigrant rights activists who have been disappointed in the high number of deportations under Obama’s watch that prompted one prominent activist to call the president the “deporter in chief.”

Obama began his address Thursday began with an emphasis on border security, stressing that his program is simply relief from deportation and not “amnesty,” as many Republicans claim.

“All we’re saying is we’re not going to deport you,” Obama said of the millions of undocumented people who qualify and apply for relief. He added that the change in emphasis will allow more resources to be devoted to border security. “If you plan to enter the U.S. illegally, your chances of getting caught and sent back just went up,” he said.

Obama then shifted his matter-of-fact tone to acknowledge the human story behind the immigration issue. “For all the back and forth in Washington, we have to remember that this debate is about something bigger,” he said. “It’s about who we are as a country and who we want to be for future generations. Are we a nation that tolerates the hypocrisy of a system where workers who pick our fruit and make our beds never have a chance to get right with the law? Or are we a nation that gives them a chance to make amends, take responsibility, and give their kids a better future?

“Are we a nation that accepts the cruelty of ripping children from their parents arms? Or are we a nation that values families and works together to keep them together?”

To qualify for relief under the new rules, an undocumented immigrant must have lived in the United States for at least five years and have a child who is either a U.S. citizen or legal permanent resident. After registering, undergoing a criminal background check and paying taxes, these immigrants will be able to stay in the U.S. for three years without fear of deportation. Some of the estimated 3.7 million parents who will qualify will also be able to apply for work permits, according to the Washington Post. After three years, it will be up to the next administration whether to extend the program.

The president’s plan will also expand a popular 2012 program, Deferred Action for Childhood Arrivals (DACA) that gives deportation relief to young immigrants brought to the country as children. The administration is lifting an age cap for eligibility under DACA and moving up the date by which an immigrant must have arrived in the U.S. to January 1, 2010. The president is also extending the program from two years to three.

Immigrants’ rights advocates had hoped the administration would also grant deferred action to the parents of DACA recipients, but a memo from Justice Department’s Office of Legal Counsel released Thursday showed the administration did not believe it had the legal authority to do that.

Obama’s executive action program also includes streamlining the Department of Homeland Security’s legal immigration programs so that high-skilled workers and their families can come to the United States more easily. It also allocates more federal resources to border security and makes deporting criminals a top priority, as opposed to pursuing law-abiding immigrants. “We’re going to keep focusing resources on actual threats to our security,” Obama said Thursday. “Felons, not families; criminals, not children; gang members, not a mom who’s working hard to provide for her kids.”

Obama is also ending the controversial Secure Communities program that allowed federal immigration officials to pick up undocumented immigrants from local jails and put them on the path to deportation. That program is being replaced with one that will focus on deporting undocumented immigrants who are convicted criminals.

The order does not have a specific program for the large population of undocumented agriculture and food processing workers in the United States, many of whom do not have children in the U.S. Still, the United Farm Workers union estimates that at least 250,000 undocumented agriculture workers will be apply under the new program. “This is the biggest victory for immigrants and their allies in the past 25 years,” said Frank Sharry, executive director of the immigrants’ rights group America’s Voice. “We rejoice with the millions who can come forward, get a work permit and live without fear.”

“What the president is doing is a first step. It’s an initiation of a process to heal our broken immigration system. But the people who have to finish the job is the Congress of the United States,” Representative Luis Gutierrez, D-Illinois, one of the most forceful voices for immigration reform in Congress, said on MSNBC Thursday night.

Conservative activists and Republicans decried the president’s announcement Thursday night. “This is an unprecedented assault on the Constitution, the separation of powers, and the rule of law in the United States,” activist Jenny Beth Martin of the Tea Party Patriots said in a statement before Obama’s announcement. “Despite the President’s assurance that he is ‘not an emperor,’ that’s exactly what he’s acting like.”

Republicans on Thursday echoed the opinion that Obama is overstepping his legal authority almost word for word. "The President has said before that he’s not king and he’s not an emperor," House Speaker John Boehner, R-Ohio, said in a YouTube video Thursday. "But he’s sure acting like one."

Republicans have sworn to take action against the President’s action but it’sunclear what authority they have to stop it. Some members of Congress have pushed to cut funding for Obama’s orders, but much of the program is expected to be administered by an agency not funded directly by Congress.

Obama insisted in his speech that his actions are lawful and challenged Republicans to pass a bipartisan immigration bill so that his program will no longer be necessary. The Senate passed a bipartisan comprehensive reform bill in June 2013 but the House of Representatives failed to act on similar legislation.

“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,” Obama said. “Pass a bill.”