President Donald Trump on Monday declared that his government would no longer treat the U.S.-born children of people who entered the country illegally as citizens, signaling his intent to essentially ignore the constitutional guarantee of birthright citizenship in a move that’s already drawn legal challenges.

His order directed federal agencies not to issue citizenship documents to such children, starting in 30 days.

It flew in the face of the guarantee, rooted in common law and enshrined in the Constitution for more than 150 years, that anyone born in the U.S. is automatically an American citizen.

In the executive order, Trump said he would interpret the 14th Amendment differently than had been done in the past, arguing that it “has never been interpreted to extend citizenship universally to everyone born within the United States.”

On Tuesday, attorneys general from at least 22 states sued Trump to block an executive order.

The order would mean that citizenship would not be extended to a child whose mother and father are not authorized to be in the U.S. at the time of birth.

But because birthright citizenship is guaranteed by the 14th Amendment to the Constitution, such an order would face major legal challenges. Any change to the Constitution requires supermajority votes in Congress, and then ratification by three-quarters of the states.

Here’s what you need to know.

The Constitution guarantees birthright citizenship

The 14th Amendment, ratified in 1868, says: “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.”

The part about jurisdiction creates a very narrow exception that has until now essentially applied only to children of accredited foreign diplomats. Other than that, the citizenship or immigration status of a person’s parents has not been held to have any effect on this right.

Trump can’t abolish birthright citizenship by himself

Presidents cannot amend the Constitution on their own, and any executive order to restrict or abolish birthright citizenship is almost certain to be challenged in court as a violation of the 14th Amendment.

But Trump is interpreting the jurisdiction language in the amendment to exclude “the children of illegal aliens born in the United States.” Until now, the overwhelming scholarly and legal consensus has been that such an interpretation would have little or no chance of winning in court.

Some legal scholars think such arguments will continue to be nonstarters in the courts. But the idea that the Supreme Court may at some point find arguments for restricting birthright citizenship persuasive is “no longer laughable,” said Amanda Frost, a University of Virginia law professor and an expert on immigration and citizenship law.

Limiting birthright citizenship was the consensus position among GOP presidential candidates in the 2024 election, and at least one federal judge has indicated a willingness to consider it.

“I don’t think it’s inconceivable, which is what I would have said in 2019,” Frost said.

By directing federal agencies to deny the children of immigrants who are in the U.S. illegally citizenship-affirming documents like Social Security cards and passports, the Trump administration is effectively ordering them to be cut off from government services like public schools, health care, nutrition and housing benefits.

Other countries have birthright citizenship

Thirty-three countries and two territories — nearly all in the Western Hemisphere, including Mexico and Canada — have unrestricted birthright citizenship similar to that of the United States, according to a tally by the World Population Review. Another 40 have restricted versions of the right. It may apply, for example, only to children of legal residents or of parents born in the country. Or it may exclude refugees.

Critics of birthright citizenship say it encourages migration

Each year, thousands of pregnant women from other countries enter the United States on a valid visa, give birth to children who automatically gain American citizenship, and then take the babies back home or to a third country. The practice, called “birth tourism,” is legal as long as the mom obtains a visa truthfully and heeds its terms.

Trump and his supporters, however, complain about expectant mothers who enter the country to give birth to what they derisively call “anchor babies” — children whose U.S. citizenship would give the family access to public benefits and a foothold toward legal residence.

The Migration Policy Institute estimates that, as of 2019, about 4.7 million American-born children under 18 were living with a parent who was living in the country illegally — about 7% of all children in the United States. But studies have found that a vast majority of such children did not cross the border in utero. The Pew Research Center estimated in 2022 that about 5 out of 6 U.S. children of immigrants living in the U.S. illegally were born two years or more after their parents entered the United States.