Maine Attorney General Aaron Frey has joined a multistate lawsuit challenging President Donald Trump’s order to deny citizenship to children born in the United States to noncitizens.

The suit — filed in U.S. District Court in Massachusetts by Frey and attorneys general in 17 other states — follows a similar lawsuit filed in New Hampshire by the American Civil Liberties Union of Maine and other civil rights and immigrants’ rights advocates.

Both suits argue that Trump’s executive order violates the 14th Amendment to the Constitution, which guarantees citizenship to children born in the United States. The suits also say the order violates the Immigration and Nationality Act and longstanding U.S. Supreme Court precedent.

“It was anticipated that the president would issue this unconstitutional block on citizenship, but that does not make it any less disappointing,” Frey said in a written statement Tuesday. “The election did not change the Constitution and legal action is required to remind the president that his oath is to uphold that sacred document, not rewrite it.”

Trump’s order relies on a different interpretation of the Constitution’s 14th Amendment, which reads: “All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States.”

Trump’s order says citizenship is not automatic if a child’s mother is not lawfully present, asserting the child is therefore not subject to U.S. jurisdiction. The order says it takes effect 30 days after its issuance.

A White House official dismissed the challenges as “nothing more than an extension of the left’s resistance,” The Associated Press reported.

“Radical leftists can either choose to swim against the tide and reject the overwhelming will of the people, or they can get on board and work with President Trump,” White House deputy press secretary Harrison Fields said.

But legal scholars and those challenging the law say it’s clear that a president cannot overturn centuries of constitutional precedent with an executive order.

Alex Nowrasteh, vice president for economic and social policy studies at the pro-immigration Cato Institute, told The Associated Press last month that birthright citizenship can’t be ended by executive order.

“The law and judges are near uniformly opposed to his legal theory that the children of illegal immigrants born in the United States are not citizens,” Nowrasteh said.

Birthright citizenship has been upheld twice by the U.S. Supreme Court, Frey’s office said.

Members of Maine’s congressional delegation from both parties said they agree with those challenging the order.

If Trump’s order survives, children of noncitizens born in the U.S. would live under the threat of deportation and would lose eligibility for a wide range of federal benefits — including their ability to obtain a Social Security number, to vote and to run for certain offices — Frey’s office said.

In addition, the order would cause states to lose federal funding for programs they administer, including Medicaid, the Children’s Health Insurance Program, and foster care and adoption assistance programs, all of which depend at least in part on the immigration status of the person being served, the AG’s office said.

“States will also be required — on no notice and at considerable expense — to immediately begin modifying their operation and administration of benefits programs to account for this change, which will require significant burdens for multiple agencies that operate programs for the benefit of the states’ residents,” the statement said.

The ACLU said many expectant couples across the U.S. are now fearing what will happen to their newborns, citing an example of a New Hampshire couple who are awaiting a ruling on their asylum application.

“Denying citizenship to U.S.-born children is not only unconstitutional — it’s also a reckless and ruthless repudiation of American values,” Anthony Romero, executive director of the ACLU and lead attorney in the case, said in a written statement.

“Birthright citizenship is part of what makes the United States the strong and dynamic nation that it is. This order seeks to repeat one of the gravest errors in American history, by creating a permanent subclass of people born in the U.S. who are denied full rights as Americans. We will not let this attack on newborns and future generations of Americans go unchallenged.”

The ACLU, state chapters in New Hampshire and Massachusetts, the Asian Law Caucus, State Democracy Defenders Fund and the Legal Defense Fund joined the ACLU of Maine in filing the New Hampshire suit on behalf of organizations with members whose children born on U.S. soil could be denied citizenship under the order.

The executive order is “completely new and unprecedented,” Cody Wofsy, deputy director of the ACLU’s Immigrants’ Rights Project, said  in a virtual news conference Tuesday, so it’s hard to say what exactly it would mean for the children who will be born after the order takes effect and whether they would be subject to deportation.

“Nobody really knows how any of this will work, which is why this is so chaotic and cruel and why there is so much fear and uncertainty for families around the country,” he said. “That said, the reason children born in the United States can’t be deported is because they are citizens. If you’re taking that away, it stands to reason that they would be subject to deportation.”

He said it’s clear that “thousands and thousands of babies” would be impacted by the order.

Members of Maine’s congressional delegation reacted to the order Tuesday by saying the 14th Amendment guarantees birthright citizenship.

“The 14th Amendment to the Constitution provides that if you are born in America, you are an American citizen,” Republican Sen. Susan Collins said in a statement. “The president’s use of an executive order to deny birthright citizenship in certain circumstances will be challenged in court.”

Rep. Chellie Pingree, D-1st District, said in a written statement Tuesday that she was happy to see the ACLU and state of Maine “not waste any time” in challenging Trump’s order.

“The 14th Amendment is crystal clear: ‘All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside,'” Pingree said. “President Trump’s attempt to end birthright citizenship is flagrantly unconstitutional — and an egregious overreach.” 

A spokesperson for Rep. Jared Golden, D-2nd District, said in a statement that, “The right of citizenship to anyone born in this country is clear as day in the 14th Amendment, and it has been upheld by the Supreme Court.”

A spokesperson for Sen. Angus King, an independent, said the senator’s legal and policy team is still working on an analysis of the dozens of executive orders Trump signed Monday.

Trump’s executive order follows up on a key promise the president made during his campaign and was one of several actions that triggered pushback Tuesday.

In addition to the multistate lawsuit that Maine is part of and the New Hampshire suit, federal lawsuits have also been filed by a separate group of four western states in Washington and by immigration groups in Boston on behalf of expectant mothers.