A federal judge Thursday blocked President Donald Trump’s executive order outlawing birthright citizenship —the policy automatically giving citizenship to anyone born in the U.S.—and declared it “blatantly unconstitutional,” as legal experts widely believe the president does not have the power to change the policy on his own.

According to Donald Trump’s Agenda 47, the President-elect announced his plan to “sign an executive order on Day One to end automatic citizenship for children of illegal aliens.”