The FCO concluded that this practice is neither justified under the General Data Protection Regulation (GDPR) nor appropriate under competition law standards applicable to monopolists.

He gave Facebook four months to present a "concept" for compliance and a year to implement it.

If it fails, Facebook will have to change how it processes data internally for German users. Facebook has already announced that it will appeal the decision.

The landmark ruling also means that users who refuse permission for their data to be merged will not be shut out of Facebook services as a result.

The FCO considers the combining of Facebook data with "non-Facebook" data an exploitative abuse because users have to agree to what FCO President Andreas Mundt refers to as a "practically unrestricted collection" of non-Facebook data if they want to use the service.

Facebook said the German regulator had confused the company's "popularity" with the concept of being "dominant" in the market for the purposes of competition law.

Vinje said it would be tough for Facebook to persuade the court that the Cartel Office's definition of the market for social media, and its dominance, were misguided.

Twitter's ad revenues soar but its user growth issues loom large
All of that came alongside Twitter's announcement on Thursday that it's changing its user metrics in earnings releases. The company said costs grew primarily because of hiring and expenses related to video content and infrastructure.

The German regulator also noted that Google+ would be shutting down in April of 2019 and that Facebook's other competitors like Snapchat, YouTube, and Twitter only offer "parts of the services" that Facebook does.

Facebook has an estimated 23 million daily active users in Germany, giving it a market share of 95%, according to the cartel office. While it has not given many details, CEO Mark Zuckerberg said in a conference call recently that the idea is to help users message people more easily, without having to navigate different platforms and lists. Ireland's data privacy regulator, which takes charge of European privacy probes involving Facebook, asked for an "urgent briefing" last month and said it will be "very closely scrutinizing Facebook's plans as they develop".

Facebook hit back at the ruling in a blog post, noting that collecting such data allows it to display better targeted ads to its users, as well as making it easier to identify fake and harmful accounts. In addition to inviting community group leaders to the summit, Facebook for the first time this year also invited leaders of local business and nonprofit groups.

The ruling will apply not just on Facebook, but across WhatsApp and Instagram - both of which are owned by the company, and will soon be integrated by Facebook to share messaging services. If Facebook does not comply with the FCO's decision and continues its practices, the FCO can impose penalty payments.

European regulators have always been concerned about Facebook's plans to deepen the integrating of WhatsApp. having previously fined Facebook 110 million euros for failing to tell them about the ability to combine the data when they examined the deal.

Vancouver-based online publication The Tyee reported on January 30 on Facebook's dealings with Royal Bank, prompting queries from parliamentarian Charlie Angus to Canada's privacy commissioner at the January 31 committee meeting in Ottawa.

'The only choice the user has is either to accept the comprehensive combination of data or to refrain from using the social network, ' it said in its judgment. Users must agree to the terms or be excluded from the social network, a hard situation that can not be considered voluntary consent, as required under the law. Facebook is becoming more and more indispensable for advertising customers.