By David G. Savage

The Supreme Court on Tuesday agreed to decide the legal fate of President Barack Obama's sweeping immigration program and rule on whether he has the power to offer "lawful presence" and a work permit to more than 4 million people living here illegally.

The justices voted to hear an appeal from Obama's lawyers, who are challenging decisions by a federal judge in Texas and the U.S. 5th Circuit Court of Appeals that blocked his immigration order from taking effect.

The announcement sets the stage for what promises to be one of the most significant and politically charged immigration decisions in the court's history, coming in the midst of the 2016 presidential race.

Three years ago, the justices dealt a defeat to conservative states that sought to crack down on illegal immigrants. They rejected the key provisions of an Arizona law that would have empowered its police to stop, question and arrest people who could not show they were citizens.

By a 5-3 vote, the justices said the president and his executive officers have "broad discretion" over immigration policy, including enforcement and deciding who should be arrested and deported.

Now, the question is whether the president may use that discretion to give several million otherwise law-abiding immigrants a temporary shield from deportation. In 2012, Obama gave this "deferred action" status to about 600,000 young people who were brought to this country illegally as children. This benefit for so-called dreamers went largely unchallenged.

In November of 2014, Obama went further and offered deportation deferral to more than 4 million parents who had a legal son or daughter in this country and who had lived here illegally since since 2010. They are "hard-working people who have become integrated members of American society," said Homeland Security Secretary Jeh Johnson in announcing the Deferred Action for Parents of Americans, or DAPA. He said the government would rather focus on deporting criminals, gang members or terrorists.

Once eligible persons came forward and passed a background check, they would be offered a work permit and would become eligible for some federal benefits, including Social Security, Medicare and the earned income tax credit.

Several hundred thousand additional immigrants could qualify for deferral under a separate expansion of the program focused on the dreamers.

But Obama's order has not gone into effect and probably won't unless the Supreme Court rules in the president's favor.

Lawyers for Texas and 25 other Republican-led states sued in a federal court in the border town of Brownsville, Texas, and they successfully argued the president had overstepped his authority.

This "assertion of unilateral executive power" violates the Constitution's "separation of powers," said Texas Solicitor Gen. Scott A. Keller. If Obama can defy Congress and decide on his own not to enforce the laws against illegal immigration, future presidents could decide on their own not to enforce laws on the environment, taxes or civil rights, he said.

In his appeal on Obama's behalf, U.S. Solicitor Gen. Donald Verrilli said the Texas lawsuit should be thrown out because the 26 Republican states have no authority to interfere with immigration policy. The DAPA order "does not regulate states or require states to do (or not do) anything," he said.

Blocking Obama's plan from taking effect "will force millions of people_who are not removal priorities ... and who are parents of U.S citizens and permanent residents _ to continue to work off the books, without the option of lawful employment to provide for their families," he said.

The case could turn on a procedural issue of "standing." Verrilli said Texas has cited no "injury" in its lawsuit, except the state's cost of providing drivers' licenses to immigrants. But Verrilli said that since Texas chose on its own to partially subsidize the cost of issuing licenses rather than forcing applicants to bear the entire cost, the state cannot now use this policy as the basis for its complaint.

Separately, California, Illinois, New York and 12 other Democratic-led states joined the case on Obama's side. They say it will "further the public interest by allowing qualified undocumented immigrants to come out the shadows, work legally and better support their families."

The two sides in the legal fight disagree even on how to describe the orders at issue. Obama's lawyers say the DAPA order is mere "guidance" and "a general statement of policy," not an official regulation. Moreover, no immigrant would have any legal rights and their "lawful presence" would be determined on a "case-by-case basis."

By contrast, the Texas lawyers say Obama seeks "one of the largest changes in immigration policy in our nation's history" affecting potentially millions of people. They concede federal agents may spare these people from deportation, but giving them a "lawful presence" and a work permit amounts to changing the law. "There is no constitutional or statutory authority for such a change," they said.

The court will likely hear arguments in United States vs. Texas in April and hand down a ruling near the end of June.

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