President Donald Trump launched his sweeping immigration crackdown on Monday which included an order reinterpreting birthright citizenship, a principle that has been recognized in the United States for more than 150 years.

Attorneys general in 18 states sued Tuesday to block the order, saying birthright citizenship cannot be undone with the stroke of the president’s pen.

Immigration rights groups, including the American Civil Liberties Union, sued the Trump administration soon after the president signed an executive order on immigration that would end birthright citizenship for children born in the U.