A federal judge preemptively blocked a landmark state law that would have required online companies to verify the ages of people in ads offering "adult services," which range from thinly veiled ads for prostitution, as well as legal, but kinky, services.

U.S. District Judge Ricardo Martinez on Tuesday stopped the Washington state law from taking force this Thursday in a suit brought by Village Voice Media – the operator of Backpage.com. The company claims the measure violates the First Amendment and the Communications Decency Act of 1996.

The judge ruled (.pdf) briefly that Backpage "has shown a likelihood of success on the merits of its claim."

Backpage asserted in its complaint (.pdf) that the law "means that every service provider – no matter where headquartered or operated – must review each and every piece of third-party content posted on or through its service to determine whether it is an 'implicit' ad for a commercial sex act in Washington, and whether it includes a depiction of a person, and, if so, must obtain and maintain a record of the person's ID. These obligations would bring the practice of hosting third-party content to a grinding halt."

The company claimed the law, which was hailed by child-protection advocates as the first-of-its kind when it passed in February, "applies not only to online classified ad services like Backpage.com, but also to any website that allows third parties to post content, including user comments, reviews, chats, and discussion forums, and to social networking sites, search engines, internet service providers, and more."

Penalties include fines of up to $10,000 and five years imprisonment.

Liz McDougall, general counsel for Village Voice Media, said "We believe human trafficking is an abomination that must be stopped. But SB 6251 is not the answer."

Judge Martinez blocked the law from taking force for at least two weeks, pending further litigation.

"On behalf of the people of Washington state, and on behalf of human trafficking victims everywhere, we will forcefully defend this groundbreaking law," said state Attorney General Rob McKenna.

Village Voice Media owns 13 print weeklies nationwide. Its Backpage.com site is a Craigslist-like service, and includes links for "dating," and adult services for "escorts," "body rubs," "stripper," d"dom & fetish" and more.

Craigslist in 2010 terminated its "adult services" section after an ongoing campaign against it for facilitating child exploitation and prostitution, despite having made multiple compromises with advocates.