Trump’s executive order, signed in January, seeks to deny citizenship to children who are born to people who are living in the U.S. illegally or temporarily. It is part of the hard-line immigration agenda of the president, who has called birthright citizenship a “magnet for illegal immigration.”

The class action lawsuit is the first major legal test of Trump’s order since the justices determined lower court judges could not place universal injunctions on federal policies. The class action will include all children who would be affected by the order, but does not include their parents, as the plaintiffs originally wanted.