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.
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 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.
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.
The lawsuit filed on Monday seeks to stop Trump acting on his emergency declaration to build the wall, saying the president does not have the power to divert funds approved by Congress to pay for his project.
It says Trump’s decision is “unconstitutional and unlawful” and that “by the president’s own admission” an emergency declaration is not necessary.
“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,” California Attorney General Xavier Becerra said.
Joining California in the lawsuit were Colorado, Connecticut, Delaware, Hawaii, Illinois, Maine, Maryland, Minnesota, Nevada, New Jersey, New Mexico, New York, Oregon, Virginia and Michigan.
The states – all of them but Maryland governed by Democrats – say the lawsuit aims to protect their residents, natural resources and economic interests. They argue that Mr Trump’s order to divert funds would cost them millions of dollars.
The White House has not commented on the lawsuit, filed in the court for the Northern District of California.