A group of 16 states in America - led by California - are suing President Donald Trump's government, over his decision to declare an emergency to raise money for the Mexican border wall that he has promised his voters.
It comes days after Mr Trump used emergency powers to allow him to bypass the usual process of making rules and getting money.
He declared a national emergency, and under these rules, Mr Trump can take money from military or disaster relief budgets to pay for the wall.
According to the president, there is a migration crisis at America's southern border, but this claim has been rejected by migration experts.
How to pay for the wall
The wall has been one of Trump's biggest campaign promises. He has been in talks with the government for months to get funding.
How to pay for the wall caused a standoff within Congress at the end of last year - the body which creates, debates and makes laws in the United States. It led to the longest government shutdown in American history and a refusal to pay for the wall.
Mr Trump said his new plan to declare an emergency would allow him to get almost $8bn (£6.1bn) for the wall which is a lot less than the $23bn (£17.8bn) estimated cost over all.
So why are states suing?
Californian Attorney General - Xavier Becerra - said his state was taking President Trump to court "to block his misuse of presidential power".
He continued "We're suing President Trump to stop him from unilaterally robbing taxpayer funds lawfully set aside by Congress for the people of our states."
Other states involved are Colorado, Connecticut, Delaware, Illinois, Maine, Minnesota, Maryland, Nevada, New Jersey, New Mexico, New York, Oregon, Hawaii, Virginia and Michigan.
The states argue that President Trump's order to move money around to pay for the wall would cost them millions of dollars.
The court action should temporarily stop Mr Trump from getting the money until it's debated in court.