A federal judge crucified the sheriff for the nation's second-most populous county Friday, ordering Illinois, Cook County Sheriff Thomas Dart to back off on its attacks on Backpage.com's sex ads—attacks that could soon put the classifieds portal out of business.

In a case testing the First Amendment and federal laws protecting Web operators for the speech of their users, Backpage sued Dart after he coerced Visa and Mastercard to refrain from doing business with the classifieds portal. Dart labeled the company a "sex trafficking industry profiteer" (PDF) because of its adult ads.

Backpage claimed in a Tuesday lawsuit (PDF) that Dart's actions amount to "an informal extralegal prior restraint of speech."

US District Judge John Tharp Jr. agreed in a Friday ruling (PDF) ordering the sheriff to cease the attacks.

The judge said Dart wrongly used his office and penned letters to essentially threaten the credit card companies to refrain from doing business with Backpage, despite an 11-year-business relationship the companies had with Backpage. The judge boiled down the issue to two questions: whether Dart's letters "constitute a threat" and whether the credit card companies "involuntarily withdrew" business from Backpage.

"The plaintiff has a better than negligible—but not certain—chance of proving that both answers are 'yes,'" the judge ruled, ordering a hearing on the matter for July 28.

The judge added that "Dart's informal lobbying of the credit card companies violated the First Amendment by imposing an informal prior restraint on the advertisements hosted by Backpage.com."

The company says it cannot last much longer without the credit card companies' transactions. On July 1, just days after sending letters to Visa and MasterCard, Dart announced that the companies had ceased doing business with Backpage. Backpage sued in hopes of getting Dart to retract his letters to the credit card companies. American Express had voluntarily stopped doing business with Backpage months ago.

The judge did not immediately order Dart to retract the letters, but instructed him to refrain from his anti-Backpage campaign. More litigation is expected.

Dart's letters to the credit card companies, on official sheriff's letterhead, had requested "that your institution immediately cease and desist from allowing your credit cards to be used to place ads on websites like Backpage.com, which we have objectively found to promote prostitution and facilitate online sex trafficking."

The letters challenged the credit card companies to find an ad in the "Adult Escort" section "that is not selling sex."

Dart wrote that the financial institutions "have the moral, social and legal right" to combat prostitution.

Dart attacked Craiglist's "adult services' ads years ago. But in 2010, Craigslist caved to pressure and removed that section.

Liz McDougall, Backpage's general counsel, said in an statement that the ruling "is an important reaffirmation of the critical role of the Internet in free speech and the continued evolution of e-commerce. It serves also as an emphatic reminder that government officials cannot undertake to destroy websites even when they disagree with hosted speech."

Listing image by Cook County Sheriff's Office