A Honduran woman, holding her 1-year-old child, surrenders to U.S. Border Patrol agents Monday near McAllen, Tex. (David J. Phillip/AP)

Seventeen states and the District of Columbia asked a federal judge on Tuesday to bar the Trump administration from separating children and their parents who enter the United States illegally at the Southwest border, asserting in a lawsuit that the practice was “an affront to States’ sovereign interests in enforcing their laws governing minimum standards of care for children.”

The suit, filed in federal district court in Washington state, adds to the growing legal morass surrounding the administration’s decision to prosecute every person who illegally crosses into the United States — even if that means separating children from their parents. While President Trump late last week sought to end the separations with an executive order, the states argued that the directive was “illusory” and offered no guarantee the administration would not try again.

That threat was particularly acute, they argued, because the administration “lacks both the capacity and the legal authority to detain families together for indefinite periods of time, which is what the Order contemplates as the alternative to separating families.”

The Justice Department recently asked a judge to modify an old legal settlement so that they could detain migrant families together for longer periods of time — though it is unclear whether the judge will accede to their request. If the government’s bid is denied, it is unclear how officials might handle parents and children who enter the United States without allowing them to be released into the country.

The lawsuit was joined by Washington, California, Maryland, Oregon, New Mexico, New Jersey, Iowa, Illinois, Minnesota, Rhode Island, New York, Vermont, North Carolina, Delaware, Massachusetts, Pennsylvania, Virginia and the District of Columbia. While it is not the first legal action over family separations, it could be significant.

Federal courts, based on challenges from states, have blocked other controversial policy changes proposed by the Trump administration — perhaps most notably in the case of his travel ban, which ultimately went through three iterations before it was upheld by the Supreme Court on Tuesday.

In addition to blocking separations, the states asked a judge to stop officials from refusing to accept asylum applications and to order the government to “expeditiously reunite all children with parents from whom they have been separated pursuant to the Policy, unless a court of competent jurisdiction has found the parents to be unfit.”

The states asserted that as of June 20, the policy had resulted in the separation of more than 2,000 children from their parents. Customs and Border Protection has since stopped referring cases for prosecution involving parents who do not have a criminal record.

California Attorney General Xavier Becerra (D) said in a statement that the administration had “hit a new low” with the policy.

“President Trump’s indifference towards the human rights of the children and parents who have been ripped away from one another is chilling,” Becerra said. “Today we are taking the Trump Administration to court because the safety, security and well-being of our children is too important to be threatened by a heartless political maneuver.”