A coalition of 16 US states is suing the Trump administration over his decision to declare a national emergency to fund a wall on the southern border with Mexico, saying the move violated the constitution.
The lawsuit, filed in a federal court in California, said President Donald Trump's order was contrary to the Presentment Clause that outlines legislative procedures and the Appropriations Clause, which defines Congress as the final arbiter of public funds.
The move had been previously announced by the attorney general of California Xavier Becerra, who said his state and others had legal standing because they risked losing money intended for military projects, disaster assistance and other purposes.
Several Republican senators have decried the emergency declaration, saying it establishes a dangerous precedent and amounts to executive overreach.
Democrats have vowed to contest it "using every remedy available".
California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Maine, Maryland, Michigan, Minnesota, Nevada, New Jersey, New Mexico, New York, Oregon and Virginia are party to the complaint seeking an injunction.
The states "bring this action to protect their residents, natural resources, and economic interests from President Donald J. Trump's flagrant disregard of fundamental separation of powers principles engrained in the United States Constitution," the complaint said.
"Use of those additional federal funds for the construction of a border wall is contrary to Congress's intent in violation of the US Constitution, including the Presentment Clause and Appropriations Clause," the complaint continued.
It added that Mr Trump had "veered the country toward a constitutional crisis of his own making".
"Congress has repeatedly rebuffed the president's insistence to fund a border wall, recently resulting in a record 35-day partial government shutdown over the border wall dispute," the document read.
The complaint also questioned Trump's categorisation of illegal border crossings as a national emergency, saying data issued by his own administration refuted the notion.
"Customs and Border Protection ("CBP") data show that unlawful entries are near 45-year lows," it said.
"The State Department recognises there is a lack of credible evidence that terrorists are using the southern border to enter the United States. Federal data confirm that immigrants are less likely to commit crimes than are native-born Americans."
The White House says the emergency order empowers it to pull around $6.6bn from other sources, mostly already-allocated funds in the Defense Department budget.
But the lawsuit countered that tapping military funds would result in huge losses for the states' national guard units which would otherwise use the money for domestic drug interdiction and counter-drug activities as well as for law enforcement programs.
The complaint added that the Department of Homeland Security had violated the National Environmental Policy Act by failing to evaluate the environmental impact of the wall in California and New Mexico.
