The U.S. Supreme Court will rule on President Barack Obama’s decision to defer deportation for as many as 5 million undocumented immigrants, agreeing to hear the administration’s appeal on one of the most contentious issues of his presidency.

The court will hear arguments in April, setting up a likely late-June ruling that will stoke what is already a fiery immigration debate in the presidential campaign.

A federal appeals court said Obama overstepped his authority in ordering the plan, which would let millions of immigrants apply for a reprieve from deportation and get work permits. The program, announced in November 2014 but yet to take effect, is being challenged by Texas and 25 other states, almost all led by Republicans.

Obama’s legal team said the appeals court’s “unprecedented and momentous” decision would strip the president of longstanding powers and give states an unwarranted right to challenge federal immigration policies in court.

“The court of appeals’ judgment enjoins nationwide a federal policy of great importance to federal law enforcement, to many states, and to millions of families with longstanding and close connections with this country,” U.S. Solicitor General Donald Verrilli argued in the appeal.

Obama acted on his own to address the status of some of the country’s 11 million undocumented immigrants after Congress reached a stalemate in efforts to pass a comprehensive overhaul of immigration laws. People whose children are either U.S. citizens or legal permanent residents, and who meet other requirements, could get relief from deportation for three years. Those individuals, who are primarily from Mexico and Central America, wouldn’t be given an easier path to citizenship.

The president says the program is simply a broader exercise of his accepted power to set priorities in deciding who should be deported.

“We are confident that the policies will be upheld as lawful,” Assistant White House Press Secretary Brandi Hoffine said in an emailed statement. She said the deferred deportation plan “will provide greater opportunities for immigrants to contribute to our society” and will make communities safer.

The decision to hear the case shows that “the Supreme Court recognizes the importance of the separation of powers,” said Texas Attorney General Ken Paxton, who is pressing the case against the administration.

“The court should affirm what President Obama said himself on more than 20 occasions: that he cannot unilaterally rewrite congressional laws and circumvent the people’s representatives,” Paxton said.

Republicans in Congress, and many of those running for president, say Obama’s executive actions amount to unfair amnesty for people who broke the law to enter or remain in the country. In March 2015, hard-line party members threatened to shut down the Homeland Security Department unless Congress blocked Obama’s plan.

Immigration is a top issue in the 2016 presidential campaign and may influence the political loyalties of Hispanics, a fast-growing ethnic group.

Republican presidential candidate Donald Trump is pushing the most far-reaching proposals on immigration, saying he would deport the 11 million undocumented immigrants in the United States, temporarily halt immigration by Muslims, and turn back Syrian refugees.

In challenging Obama’s orders, Texas and its allies say federal immigration laws set out detailed rules for deportation and don’t give the president authority to shield such a large category of people.

Major decisions on immigration policy “must include the people’s elected representatives in Congress,” Texas argued. “Executive agencies are not entitled to rewrite immigration laws.”

The high court said it will consider both the appeals court’s reasoning, which turned on the president’s statutory powers, and a separate line of argument over the president’s constitutional authority. The Texas-led states say Obama violated his constitutional duty to “take care that the laws be faithfully executed.”

Fifteen other states and the District of Columbia are among those backing the administration in the case.

The Supreme Court case may turn on a series of questions over whether the states had the right to challenge the policy.

The 2-1 appeals court decision said the states have what lawyers call “standing” to sue because the plan would cost them millions of dollars. The court said Texas would be in the position of providing subsidized driver’s licenses for potentially hundreds of thousands of people.

The administration argued that a state can’t acquire standing to sue through a “voluntary decision to extend a subsidy” to undocumented immigrants spared from deportation. Texas and the other states countered that the plan will also require additional spending on health care, law enforcement and education.

Obama administration lawyers also say the states’ claims are barred by the U.S. Administrative Procedure Act, which allows suits over actions taken by federal agencies only in particular circumstances, even if a challenger has standing.

Sen. Roger Wicker of Mississippi, chairman of the National Republican Senatorial Committee, said in an interview he sees the case as ensuring Congress’s role in the balance of power.

“I would certainly expect to win that case and for the court to make it clear that the president is grossly overreaching,” Wicker said.

Senate Minority Leader Harry Reid, a Nevada Democrat, said in a statement that Obama relied on “well-established constitutional authority” and acted only after House Republicans refused to take up immigration legislation passed by the Senate in 2013.

“President Obama’s decision to set enforcement priorities focused limited resources on the removal of individuals who pose a threat to our national security and public safety, not hard- working families,” Reid said.