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.
Mr Trump made the declaration on Friday to bypass Congress after it refused to approve $5.7bn (£4.4bn) for the wall.
The states say they want to block his “misuse of presidential power”.
The Democrats oppose funding Mr Trump’s barrier, a key campaign pledge, and have vowed to contest his plan.
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.