A coalition of 16 US states led by California is suing President Donald Trump's administration over his decision to declare a national emergency to obtain funds for building a wall along the US-Mexico border.
The lawsuit filed in US District Court for the Northern District of California came just days after Trump invoked emergency powers on Friday after Congress declined to fulfil his request for $US5.7 billion (NZ$8.3 billion) to help build the wall that was his signature 2016 campaign promise.
His move aims to let him spend money appropriated by Congress for other purposes.
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"Today, 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 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. For most of us, the Office of the Presidency is not a place for theatre," added Becerra, a Democrat.
Three Texas landowners and an environmental group filed the first lawsuit against Trump's move on Friday, saying it violates the Constitution and would infringe on their property rights.
The legal challenges could slow down Trump's efforts to build the wall, which he says is needed to check illegal immigration and drug trafficking, but will likely end up at the conservative-leaning US Supreme Court.
In a budget deal passed by Congress to avert a second government shutdown, nearly $US1.4 billion was allocated toward border fencing. Trump's emergency order would give him an additional $US6.7 billion beyond what lawmakers authorised.
In television interviews on Sunday and Monday, Becerra said the lawsuit would use Trump's own words against him as evidence there is no national emergency to declare.
Earlier, Trump had said he knew that he did not need to declare an emergency to build the wall, a comment that could now undercut the government's legal argument.
"Presidents don't go in and claim declarations of emergency for the purposes of raiding accounts because they weren't able to get Congress to fund items," Becerra said on MSNBC.