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.

After being sworn in as president on Monday, Jan. 20, President Donald Trump filed an executive order to terminate birthright citizenship for children of undocumented immigrants.

Trump's order directs federal agencies to stop issuing citizenship documents to U.S.-born children of undocumented mothers. It also applies to mothers in the country on temporary visas, if the father is not a U.S. citizen or permanent resident.