Plaintiffs in the ACLU’s lawsuit argue the president’s executive order banning birthright citizenship is unconstitutional.

Put simply, under Trump’s order, the children of most undocumented immigrants wouldn’t be US citizens, nor would the children of people in the country on student, work, or tourist visas. This is more than a reinterpretation of the 14th Amendment — it’s an attempt to do away with the jus soli principle that undergirds US citizenship.

Eighteen states and the ACLU filed lawsuits seeking to prevent President Trump from denying citizenship to children born in the U.S. to non-citizens.