This story was updated on Jan. 21 at 6:08 p.m. to reflect that the ACLU’s lawsuit was filed on Monday, not Tuesday. Hours after President Donald Trump issued an executive order Monday barring birthright citizenship to children of undocumented residents,

The ACLU seeks to prevent President Trump from bypassing the 14th Amendment, which granted citizenship to nearly everyone born in the United States

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.