Apple and Google They have been ordered to remove apps that can “undress” or “undress” people and told they must stop profiting from harmful technology, according to cease-and-desist letters sent to the companies seen by WIRED.

On Thursday, San Francisco City Attorney David Chiu sent legal notices to Apple and Google demanding that they remove 13 face-swapping apps, which allow users to create non-consensual AI-generated nude images, from their app stores. The letters say Silicon Valley giants should stop “aiding and abetting” the sale of explicit deepfake images and “sever” business relationships with app developers.

“Generating non-consensual intimate images is illegal, harmful and completely unacceptable,” Chiu tells WIRED. The city attorney, whose office previously took legal action against 16 popular deepfake websites, says Apple and Google have likely “made millions of dollars in fees” from apps that offer nudification, and that they should improve their moderation processes to prevent them from appearing in their stores in the first place.

“These companies have a responsibility to ensure that the apps on their platforms do not facilitate sexual abuse,” Chiu says. The city’s legal letters say California law prohibits supporting services that create deepfake pornography. The apps use in-app payments, of which the tech companies take a cut, the letters say. “The fact that some of the largest and most established technology companies in the world are facilitating this has to stop.”

Researchers have repeatedly found and reported on apps in Apple’s App Store and Google Play Store that allow people to generate sexual images using AI, including some apps classified as suitable for use by children. While new laws and bans aim to address the scourge of explicit deepfakes online, technology and social media companies are constantly directing millions of people towards this harmful technology.

Both Apple and Google have developer policies that prohibit pornography, abuse, and harassment on their platforms. They previously removed dozens of nudify and deepfake apps, following reports from researchers and journalists.

Google spokesperson Dan Jackson tells WIRED that the company has removed “hundreds” of apps with nudification features for policy violations, including the five Android apps flagged by Chiu’s office, among other measures to restrict access to them.

“Google Play does not allow apps that contain sexual content and we continually take proactive measures to detect and remove apps with harmful content,” Jackson says in a statement. “When violations are reported to us, we investigate and take swift action, which in the case of these apps has included suspending hundreds of infringing apps and restricting related search terms like ‘nudify’ from our store.”

Apple tells WIRED that developers are ultimately responsible for the content of their apps, and that those who don’t follow the rules will have their apps removed. The company also says that users can report potentially problematic apps themselves. Adam Dema, an Apple spokesperson, told WIRED in a statement that the company removed three of the apps flagged by the San Francisco city attorney and is “in the process of terminating their developer accounts from our program.” The other four developers must “address policy violations or risk being removed as well,” the company says.

“The App Store was designed to be a safe and trusted place for users, and we have always strictly prohibited apps designed to generate, distribute or consume pornography,” Dema says in the statement. “‘Nudifying’ apps go against our App Review Guidelines and we have proactively rejected many of these apps and removed many others, even when users have flagged them through our reporting tools.”