SEATTLE (AP) — The website Backpage.com and a nonprofit group that runs a popular archive of Internet sites asked a federal judge on Friday to block a Washington state law that would require classified advertising companies to verify the ages of people in sex-related advertisements.

Gov. Chris Gregoire signed the law, which passed the Legislature unanimously, to cut down on child sex trafficking. Officials hope it will become a national model for dealing with the pernicious problem; they say an estimated 100,000 juveniles are victimized by child prostitution in the U.S. every year.