A coalition of 16 US states led by California has sued President Trump’s administration over his decision to declare an emergency to raise funds for a Mexican border wall.
The lawsuit was filed in court for the Northern District of California.
It comes days after Mr Trump invoked his emergency powers to bypass Congress and secure funding for the project a key campaign pledge.
Democrats have vowed to use every remedy available to contest the decision.
The president’s announcement came after he signed a spending bill to avoid another government shutdown that granted him only $1.375bn for new border barriers.
Mr Trump said he had not needed to declare the emergency but had done so in the hope of obtaining the funds for the wall more quickly.
Analysts say these comments could undermine his legal arguments.