Germany's competition authority Bundeskartellamt has told Facebook it can only continue gathering so much data about users from beyond its app and website if it gets individuals' consent.
The watchdog has carried out a probe into the social network following concerns that members were unaware of the extent of the firm's activities.
It covered data gathered from third-party sources as well as via Facebook's other apps, including Instagram.
The US firm has said it will appeal.
Specifically, the FCO has ruled that Facebook's various services can continue to collect data, but they cannot combine it with the user's main Facebook account unless the member gives their voluntary consent.
According to FCO, collecting data from third-party websites and assigning it to a Facebook user's account is likewise only allowed if that member has given the firm permission.
The Bundeskartellamt’s decision is not yet final. Facebook has one month to appeal the decision to the Düsseldorf Higher Regional Court.