Image copyright Getty Images Image caption Migrants' rights activists demonstrated outside the court last week

The US Supreme Court has said it will consider a challenge to one of President Barack Obama's key immigration reform plans.

The plan would lift the threat of deportation from five million migrants living illegally in the US.

A coalition of 26 mostly conservative states, led by Texas, has been successful in lower court challenges.

A decision from the highest US court is expected in the early summer, just as the US election gets into full swing.

"We are confident that the policies will be upheld as lawful," said White House spokeswoman Brandi Hoffine.

President Obama announced the plan, known as Deferred Action for Parents of Americans and Lawful Permanent Residents (DAPA), in November 2014.

He justified using his presidential powers, without Congress, by saying it was in response to inaction over the issue of immigration from Congress.

Analysis - Anthony Zurcher, BBC News, Washington

This will only heighten the drama surrounding this issue as the US presidential election season shifts into high gear this summer.

If the White House wins this case, the stakes could not be higher. Hillary Clinton, the likely Democratic nominee, has already pledged to expand upon Mr Obama's unilateral efforts.

Thanks to the efforts of Republican frontrunner Donald Trump to push his party to the right on immigration policy, the Republican nominee - whatever his or her identity - will be nearly certain to reverse course from the first day in office.

If Obama loses the case, the outlook is somewhat murkier. Such a development could boost turnout of a frustrated Hispanic electorate, who largely support the Democrats.

Or it could rally conservatives who view the Supreme Court - whose future composition may be shaped by the next president - as their last bulwark against liberal power.

Image copyright Getty Images

If allowed to go forward, it would allow people who have lived in the US for more than five years and who have children who are living in the country legally to apply for work authorisation.

In announcing the plan, Mr Obama said it would allow those who qualify to "come out of the shadows and get right with the law".

Challenges to the plan began shortly after Mr Obama's announcement, with a federal court in Texas effectively putting a pause on it in February.

The Obama administration lost an appeal in November, keeping the injunction in place.

The Supreme Court will hear arguments in April and deliver its decision by late June, about a month before the Republican and Democratic parties gather for their nominating conventions.

The White House has vowed to kickstart the programme if the court backs the plan, so migrants could began enrolling before a new president takes office in January 2017.

One of the largest questions looming over the case is whether the state challengers have the right to do so.

Texas argues it will have to spend millions of dollars to provide driver's licences to people who are part of the programme.

The issue of immigration has become a controversial and polarising issue in the 2016 presidential race.

Leading Democrat Hillary Clinton has said she would maintain and expand President Obama's reforms, while her Republican counterpart, Donald Trump has said he would reverse the reforms and step up enforcement.