Attorneys general from Colorado and 21 other states filed lawsuits Tuesday to block President Donald Trump’s executive order to end birthright citizenship, a principle enshrined in the U.S. Constitution that guarantees that U.S.-born children are citizens regardless of their parents’ immigration status.

Colorado Attorney General Phil Weiser called the president’s move a violation of the constitutional rights that children born in the U.S. are entitled to.

“The idea that a president could override the Constitution with the stroke of a pen is a flagrant assault on the rule of law and our constitutional republic,” Weiser said in a news release Tuesday announcing the lawsuit.

“The executive order cannot be allowed to stand, and I will fight to ensure that all who are born in the United States keep their right to fully and fairly be a part of American society as a citizen with all its benefits and privileges.”