Attorneys general from 18 states have sued President Trump to block an executive order that refuses to recognize the U.S.-born children of unauthorized immigrants as citizens

The day after President Trump signed an executive order seeking to end birthright citizenship, 18 Democratic state attorneys general joined a legal effort to challenge the move, calling it unconstitutional.

“What the president did yesterday is unlawful, unconstitutional, and it will not stand,” said New Jersey Attorney General Matthew Platkin in an interview with NPR.

“We are a state of immigrants. Millions of people in our state have obtained their citizenship through birthright citizenship,” Platkin added. “It’s the story of our state and the story of America, and it’s enshrined in our Constitution for a reason.”

Democratic attorneys general from states including New Jersey and California, as well as the cities of San Francisco and Washington, D.C., signed onto a lawsuit filed Tuesday in Massachusetts to block the order.

At a press conference, California Attorney General Rob Bonta criticized Trump’s executive order, calling it “a terrifying tone to set for his second term” and declaring, “I have one message for President Trump: I’ll see you in court.”

Separately, the American Civil Liberties Union (ACLU) also filed a lawsuit on Monday to stop the order. “Denying citizenship to U.S.-born children is not only unconstitutional — it’s also a reckless and ruthless repudiation of American values,” said Anthony D. Romero, the ACLU’s executive director, in a statement.

The 14th Amendment, ratified in 1868 after the Civil War, states that all persons “born or naturalized in the United States, and subject to the jurisdiction thereof,” are U.S. citizens. While originally intended to establish citizenship rights for Black Americans, the amendment has been interpreted for over a century to include all children born on U.S. soil, regardless of their parents’ immigration status.

Trump’s executive order, however, argues that the amendment excludes children born in the U.S. to parents who are “unlawfully” present or have “lawful but temporary” status.

“It’s ridiculous. We’re the only country in the world that does this [grants automatic citizenship], as you know,” Trump said Monday night while signing the order. However, many countries, including Canada and Mexico, also grant some form of birthright citizenship similar to the U.S.