MasterCard will no longer allow its cards to be used in ad purchases on, following pressure for Illinois law enforcement, according to multiple reports., a classifieds site similar to Craigslist, runs ads for a variety of things and includes an “adult” section with ads for escorts, “back rubs” and strippers, among other things. The site has been criticized by many for allegedly allowing pimps and sex traffickers to solicit sex anonymously.

Cook County Sheriff Thomas Dart sent a letter to both Visa and MasterCard Monday asking them to disallow use of their cards by patrons of the site. Cook County is the second most-populous county in the U.S. and Dart has been tracking solicitations for prostitution on the site for some time.

According to the Wall Street Journal, in Dart’s letter to the two companies, he wrote that “we have objectively found [Web sites like Backpage] promote prostitution and facilitate online sex trafficking.”

“I am calling on Visa and MasterCard to do the right thing — defund this criminal enterprise,” he said in his statement issued before Mastercard’s announcement, according the Chicago Tribune. “After years of unchecked growth in the online sex trade, it has become increasingly indefensible for any corporation to continue to willfully play a central role in an industry that reaps its cash from the victimization of women and girls across the world.”

Dart has scheduled a news conference for Wednesday morning in order to discuss his efforts to work with the two credit card companies, the Tribune reported.

MasterCard representatives told media outlets Tuesday that the company has strict rules against using their cards for “illegal or brand-damaging activities.”

“When the activity is confirmed, we work with the merchant’s bank to resolve the situation,” said company spokesman Seth Eisen in a statement, according to USA Today. “Based on a request from Cook County Sheriff’s Office, we contacted Backpage’s acquiring bank about the issue. They have advised us that they are terminating acceptances at this time.”

Multiple media outlets were unable to reach Visa for comment about Dart’s request to the company.

American Express has already disallowed use of their cards on Backpage, according to USA Today.

Dart’s office told Time Magazine that Backpage sells adult ads at prices in between $5 and $17. Those ads generate roughly $9 million a month, with 1.4 million ads for sex placed just this past April. If Visa also stops allowing use of their cards on the site, users will only be able to pay with Bitcoin.

Former federal prosecutor Jeffrey Cramer told the Chicago Tribune that Dart’s actions were a “progressive” way to go after the site given the minimal legal restrictions on sites like Backpage.

“It’s hard to solve this problem under the criminal code,” Cramer said. “People are buying ads, and the owners of the Web site aren’t theoretically doing anything illegal. They are providing a forum.”