In an agreement with the National Center for Missing and Exploited Children (NCMEC) and 40 U.S. state attorneys general, Craigslist said it has begun cracking down on illegal sex-for-hire activity by requiring massage parlors, strippers and escort services to pay $5 per listing, payable by credit card. Craigslist said it would donate all proceeds from such advertising to charity.

“It raises the accountability for people posting to the category,”  Craigslist CEO Jim Buckmaster told the San Francisco Chronicle. “Our well-intentioned users don’t want to see illegal activity on the site either.”

Craigslist’s action is voluntary; sites such as Craigslist have immunity under federal law for illegal activities that might transpire between advertisers and customers. Many law-enfocement agencies chase down prostitutes on Craigslist and a few have even run prostitution sting operations. Craigslist has a long history of cooperating with law enforcement on such matters, with or without subpoenas.

Under the agreement, Craigslist will begin collecting credit-card numbers from erotic-services advertisers. It already requires advertisers to leave phone numbers, which, Buckmaster said, has reduced the volume of prostitution ads.

“Human trafficking and child exploitation are despicable crimes, and in addition to working diligently to prevent such abuse, we want to do everything we can to raise awareness among Craigslist users so that they will be even more vigilant,” Buckmaster wrote on the company blog.

On his private blog, founder Craig Newmark said, “We’ll be working together to fight predators, which includes charging in our ‘erotic services’ category. 100% of profits from this will be contributed to charity. An external accounting firm will be retained to track the details. We will NOT profit from this.”

Newmark added that Craigslist will be going after ad spammers as well. “We’ll be discussing this with ad spam technology providers and others in court. We’re not litigious, but this is a good complement to our technology efforts.”

Reactions to the news were mixed, as we would expect. Some applauded the move, other derided it as a capitulation of free speech.