Germany has announced a clampdown on Facebook's 'unrestricted' gathering of personal data from other websites.
Competition chiefs have ordered the California-based tech firm to stop combining Facebook data with user information from Instagram, WhatsApp and third-party websites unless users give their consent.
The ruling, which comes at the end of a three-year probe, will also limit data collection from external websites which have a Facebook 'like' button.
Facebook has vowed to challenge the decision, saying it had been unfairly singled out and accusing German officials of 'underestimating' the competition they faced.
Germany's anti-trust regulator said Facebook's terms and conditions forced users to accept the collection of data from multiple sources.
Announcing their decision, they said Facebook-owned services such WhatsApp and Instagram can continue to collect data, but users will have to consent before the information is assigned to Facebook accounts.
If users do not agree, the data 'must remain with the respective service and cannot be processed in combination with Facebook data,' they said.
The regulator said many people were not aware of how websites with a 'Like' button could be used to gather data linked to a Facebook account.
Some 23million Germans used Facebook every day, the agency said.
The agency's boss Andreas Mundt said: 'As a dominant company Facebook is subject to special obligations under competition law.
'In future, Facebook will no longer be allowed to force its users to agree to the practically unrestricted collection and assigning of non-Facebook data to their Facebook user accounts.
'The combination of data sources substantially contributed to the fact that Facebook was able to build a unique database for each individual user and thus to gain market power.
'In future, consumers can prevent Facebook from unrestrictedly collecting and using their data.
'The previous practice of combining all data in a Facebook user account, practically without any restriction, will now be subject to the voluntary consent given by the users.'
Responding to the decision, Facebook said German officials had 'underestimated the fierce competition we face in Germany'
The ruling would 'implement an unconventional standard for a single company', Facebook said.
They said: 'We face fierce competition in Germany, yet the [regulator] finds it irrelevant that our apps compete directly with YouTube, Snapchat, Twitter and others.
'As part of complying with the GDPR, we revamped the information we provide people about their privacy and the controls they have over their information.
'Using information across services helps to make them better and protect people’s safety.
'Using information across our services also helps us protect people’s safety and security, including, for example, identifying abusive behavior and disabling accounts tied to terrorism, child exploitation and election interference.''
This article has been adapted from its original source.
© Associated Newspapers Ltd.