A federal judge on Thursday temporarily halted President Donald Trump's executive order that seeks to end birthright citizenship in the US, criticising the directive as being “blatantly unconstitutional”.
Mr Trump on inauguration day signed an order denying citizenship for children born in the US to undocumented immigrants, or born to mothers who were in the US legally but temporarily. It was due to come into force as early as February 19.
The 14th Amendment in the US Constitution guarantees citizenship for anyone who is born in the US.
District Court Judge John Coughenour was responding to a request by lawyers in Arizona, Illinois, Oregon and Washington state to halt the order while courts consider legal cases against it.
“This is a blatantly unconstitutional order”, Mr Coughenour said, according to the Seattle Times.
He said he was bewildered when a Justice Department lawyer asserted it was constitutional, to which he responded: "It just boggles my mind."
Mr Trump's move threatens to rescind a Constitutional right that has been recognised for more than 150 years.
The 14th Amendment states: “All persons born or naturalised in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside.” The amendment also grants citizens protection from discrimination and government action that would deny equal protection of the law.
Immigration critics and Republicans argue that the provision allows for abuse by people who come to the US merely to have children with American citizenship.
Later on Thursday, Mr Trump said of the judge's decision: "Obviously we'll appeal it."
The issue is expected to wind up in the US Supreme Court because Mr Trump is trying to change a constitutional amendment through an executive order, something legal experts say he cannot do. He threatened to sign a similar order in his first presidency.
While the Supreme Court can interpret the US Constitution, major changes usually require an act by Congress that is then approval by 38 of the 50 states.
“Nothing in the Constitution grants the President, federal agencies, or anyone else authority to impose conditions on the grant of citizenship to individuals born in the United States,” the four states said in their court filing.
Another group of 18 Democratic-led states filed a separate legal case. The District of Columbia and the city of San Francisco have joined that challenge.
Mr Trump's executive order is also facing a legal challenge by the American Civil Liberties Union, which it filed on the evening of inauguration day.
Dozens of countries around the world, including most of North and South America, have birthright citizenship.