Credit card giants Visa and Mastercard said Sunday that they are investigating their business relationship with Pornhub after a prominent newspaper columnist alleged that the pornographic website shows videos of rape and underage sex.

Nicholas Kristof, opinion columnist at The New York Times, wrote Friday that Pornhub carries rape scenes, revenge pornography and other examples of explicit video taken without consent of the participants.

In a statement to The Associated Press on Sunday, Pornhub said it is “irresponsible and flagrantly untrue” to suggest that it allows images of the sexual abuse of children on its site. Pornhub added that it employs moderators to screen every upload and that it removes illegal material.

The online payment service PayPal last year stopped processing payments to Pornhub, which is owned by the pornography conglomerate MindGeek. The columnist called out other card issuers for working with the site.

In response to Kristof’s story, Visa and Mastercard said they’re investigating the matter.

“We are aware of the allegations, and we are actively engaging with the relevant financial institutions to investigate, in addition to engaging directly with the site’s parent company, MindGeek,” Visa said Sunday.

Visa added that if Pornhub is violating the law or bank policies, then the website will be prohibited from accepting Visa payments.

Meanwhile, Mastercard promised “immediate action″ if the allegations are substantiated.

“We are investigating the allegations raised in the New York Times and are working with MindGeek’s bank to understand this situation,” Mastercard said in a statement.

American Express said company policy prohibits the Amex card from being used on “digital adult content websites.”

The Associated Press contributed to this report.