California and 15 other US states have filed a lawsuit against President Donald Trump to challenge his declaration of a national emergency.

The group of states, led by California Attorney General Xavier Becerra, filed the lawsuit in the US District Court for the Northern District of California on Monday.

“We’re suing President Trump to stop him from unilaterally robbing taxpayer funds lawfully set aside by Congress for the people of our states,” Becerra said in a statement.

Trump declared a national emergency on Friday to bypass Congress and secure funding for a wall on the US southern border.

Becerra and California governor Gavin Newsom said in the statement that Trump’s claims that there is a crisis at the southern border have no factual basis and are a pretext to divert funds to finance his wall.

“President Trump treats the rule of law with utter contempt. He knows there is no border crisis, he knows his emergency declaration is unwarranted, and he admits that he will likely lose this case in court,” Becerra said.

Colorado, Connecticut, Delaware, Hawaii, Illinois, Maine, Maryland, Michigan, Minnesota, Nevada, New Jersey, New Mexico, New York, Oregon, and Virginia are joining California in filing the suit.

The argument that it is unconstitutional for Trump to circumvent Congress to fund the wall along the US-Mexico border by declaring an emergency is at the core of the legal action.

Becerra argued that the states have the standing to challenge Trump because money appropriated to them might be at risk.

“If the president is essentially stealing money that’s been allocated to go to the various states for various purposes but no longer will, we’re being harmed, our people are being harmed,” he told CNN.

The legal action follows a suit filed by progressive non-profit organization Public Citizen on Friday in a federal district court in Washington on behalf of three Texas landowners and Frontera Audubon Society, a nature park in the Rio Grande Valley.

Critics have said that Trump’s difficulties with Congress do not meet the criteria of the 1970s National Emergencies Act.

They say Trump’s admission in his Friday announcement that “I don’t need to do this” showed he was not justified in redirecting 3.6 billion dollars from military construction to the border wall.