Sixteen states filed a lawsuit Monday against the Trump administration, decrying the declaration of a national emergency along the U.S.-Mexico border as unnecessary and unconstitutional.

“On Presidents Day, we take President Trump to court to block his misuse of presidential power,” California Attorney General Xavier Becerra said in a statement.

On Friday, after months of threatening such a move, President Donald Trump strode to a lectern in the White House Rose Garden and proclaimed the emergency — his latest attempt at securing billions of dollars refused to him by Congress to build or reinforce barriers along the border.

“Walls work 100 percent,” Trump said, echoing his rhetoric from the campaign trail. Back then, he claimed Mexico would pay for the wall.

Using a national emergency — the same step presidents took during the Iran hostage crisis in 1979 and after the Sept. 11 terrorist attacks — to build a wall rankled some fellow Republicans and immediately drew criticism and threats of litigation.

Becerra called the proposal “foolish” and California Gov. Gavin Newsom described the wall as “a vanity project, a monument to stupidity.” The true emergency, Newsom argued, is the recent wildfire disaster and the people desperately in need of federal funds.

In a statement released after the suit was filed, Newsom said he intended to send a clear message to the president: “California will not be part of this political theater. We will see you in court.”

Along with Becerra, attorneys general from Colorado, Connecticut, Delaware, Hawaii, Illinois, Maine, Maryland, Michigan, Minnesota, Nevada, New Jersey, New Mexico, New York, Oregon and Virginia joined in the lawsuit, which was filed in the Northern District of California.

Administration officials say the president intends to use emergency powers to divert money allotted for other things, including military construction projects, to build or update as much as 234 miles of border fences.

Trump’s acting chief of staff, Mick Mulvaney, told reporters last week that the emergency declaration would provide an additional $6.6 billion for barriers, potentially bringing the total spending to $8 billion. (On Thursday, Congress passed a spending bill to avert another government shutdown and authorized $1.375 billion for border barriers.)

Even before the lawsuit was filed, many legal experts seized on Trump’s own characterization of the national emergency during his announcement, arguing he acted out of preference not urgency.

“I could do the wall over a longer period of time,” Trump said. “I didn’t need to do this, but I’d rather do it much faster.”

Los Angeles Times staff writers Noah Bierman and Phil Willon contributed to this report.