The change, which was first reported by Bloomberg, comes as part of a bigger update to Apple’s developer rules, which now include a lengthier section on data use and sharing.

But the new rule that really caught people’s eye was one that explicitly warns developers not to use information about contacts in order to create a “database” or sell that information to third parties. While it’s common for developers to request access to a user’s contacts — it’s how social apps can connect you with other people you know, for example — it hasn’t always been clear what happens to this data after a user grants the permission.

In a followup article, Bloomberg further points out that these changes could have some major ramifications for one of Facebook’s often overlooked apps.

Here’s the relevant section from Apple’s rules (emphasis added):

(iv) Do not use information from Contacts, Photos, or other APIs that access user data to build a contact database for your own use or for sale/distribution to third parties, and don’t collect information about which other apps are installed on a user’s device for the purposes of analytics or advertising/marketing.

That lastbit, which explicitly tells developers they can’t use their apps to track what other apps a person is using, is the part some experts have speculated is aimed directly at Facebook’s Onavo VPN service.

As Bloomberg points out, Facebook uses Onavo to gather data about what other apps it users are engaging with (some have labeled the practice as“corporate spyware”). Apple’s always frowned upon apps collecting data from each other — it’s why it has sandboxing rules in the first place — but these latest guidelines would seem to go a step further in order to prevent developers from circumventing its policies.

And though the rules don’t call Facebook out by name, Apple’s made no secret of its criticism for the social network’s privacy policies. Tim Cook haspublicly criticized Facebook (Mark Zuckerberg wasn’t pleased) and at WWDC, Apple made a big show of blocking Facebook-powered ad tracking features in Safari.

Whether the company now actually has its sites on Onavo specifically is unclear, but it’s obviously looking to stop apps that at least function similarly to Facebook’s VPN service and that’s likely bad news for Facebook.