A coalition of 16 US states led by California is suing President Donald Trump’s administration over his decision to declare an emergency to raise funds for a Mexican border wall.
The lawsuit was filed in the court for the Northern District of California.
It comes days after Mr Trump invoked emergency powers to bypass Congress and secure funding for the project – a key campaign pledge.
Democrats have vowed to contest it “using every remedy available”.
California Attorney General Xavier Becerra said they were taking President Trump to court “to block his misuse of presidential power”.
“We’re suing President Trump to stop him from unilaterally robbing taxpayer funds lawfully set aside by Congress for the people of our states. For most of us, the office of the presidency is not a place for theatre,” he added.
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The lawsuit filed on Monday seeks a preliminary injunction that would stop Mr Trump acting on his emergency declaration while a legal battle takes place in the courts, the Washington Post reported.
Mr Trump announced the plan after Congress refused funding for the wall.
The first legal challenge followed swiftly on Friday. A liberal advocacy group, Public Citizen, sued on behalf of a nature reserve and three Texas landowners who have been told the wall may be constructed on their properties.
Governor Gavin Newsom of California dismissed the president’s decision as “political theatre” while New York state’s Democratic attorney general, Letitia James, promised to “fight back with every legal tool at our disposal”.
How did Mr Trump declare the emergency?
Making the announcement in the White House Rose Garden on Friday, the president said the emergency would allow him to get almost $8bn for the wall.
This is still considerably short of the estimated $23bn cost of the wall along almost 2,000 miles (3,200km) of border.
Mr Trump accepted that he would be sued for the move, and predicted that the emergency order would lead to legal action which was likely to end up in the Supreme Court.
“We’re going to confront the national security crisis on our southern border,” he said.
“Everyone knows that walls work.”
However, the president also said that he did not need to declare the emergency but did so in the hope of obtaining the funds for the wall more quickly, but analysts say these comments could undermine his legal arguments.
What is a national emergency?
The National Emergencies Act is intended for times of national crisis. Mr Trump has claimed that there is a migration crisis at the nation’s southern border – a claim strongly refuted by migration experts.
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The largest number of illegal migrants settling in the US each year is those who stay in the country after their visas expire.
Declaring a national emergency would give the president access to special powers that effectively allow him to bypass the usual political process, and he would be able to divert money from existing military or disaster relief budgets to pay for the wall.
Emergency declarations by previous presidents have been overwhelmingly used for addressing foreign policy crises – including blocking terrorism-linked entities from accessing funds or prohibiting investment in nations associated with human rights abuses.