A federal judge in Boston has blocked an executive order from President Donald Trump that would end birthright citizenship for the children of parents who are in the U.S. illegally.

The 14th Amendment was ratified in 1868, after the Civil War, with the intention of granting full citizenship rights to freed African American slaves; its birthright citizenship clause has since been interpreted to include all U.S.-born children, regardless of parental immigration status.

Trump’s controversial executive order looks to deny citizenship to children born to noncitizens. The order has been temporarily blocked by a judge who called the move “blatantly unconstitutional.”