The Delaware Department of Justice is joining 17 states in suing the Trump administration for its order ending birthright citizenship.

Until the order, which Trump signed the same day he was inaugurated as the 47th president, the U.S. government has, at least the late 1800s, considered the child of any immigrant born on U.S. soil an automatic citizen, even to a mother in the United States illegally.

Delaware and Maryland are joining 16 other states in a lawsuit challenging President Donald Trump’s executive order aimed at ending birthright citizenship in the United States.