German watchdog accuses site of merging data from WhatsApp and Instagram into users’ Facebook accounts without consent.

Germany’s competition authority has accused Facebook of abusing its dominant market position to improperly amass third-party data on its users.

A statement released on Tuesday criticised the world’s largest social media site for collecting data via Facebook-owned services, such as WhatsApp or Instagram, and then absorbing it into users’ Facebook accounts.

“We are mostly concerned about the collection of data outside Facebook’s social network and the merging of this data into a user’s Facebook account,” said Andreas Mundt, the president of the Bundeskartellamt, or federal cartel authority.

“This even happens when, for example, a user does not press a ‘like button’ but has called up a site into which such a button is embedded,” he said. “Users are unaware of this.”

In a preliminary assessment of an ongoing administrative proceeding against Facebook, the anti-monopoly body said it was not convinced that users had consented to Facebook tracking and merging their data, a practice which it believes “violates mandatory European data protection principles”.

Some German politicians called on the competition authority to go further in its criticism: “A reprimand is not enough,” tweeted Sahra Wagenknecht, co-chair of Germany’s Left party. “Google and Facebook’s extreme market power has to be broken up by barring them from the mass theft of our data!”

Facebook denied that it dominated the market in which it operated.

“Although Facebook is popular in Germany, we are not dominant,” said Yvonne Cunnane, the company’s head of data protection.

Cunnane said competition from social platforms, such as Snapchat, YouTube, Flickr, Twitter, Google Photos or Pinterest, as well the non-success of its Slingshot, Paper and Rooms apps, showed that Facebook wasn’t enjoying a comfortably dominant market position, she said.

On data protection, Facebook said it would continue to cooperate with the competition authority and planned to introduce additional controls and provide more information security in the coming months.

Since October the company has run a large campaign in Germany – home to more than 30 million Facebook users – aimed at placating growing public concerns about online privacy.

Ads with slogans such as: “You post a picture of your children and the entire world can see it” have appeared on Facebook and YouTube, as well as in newspapers and on posters in public spaces.

The Belgian data protection authority won a court order in 2015 against Facebook to stop it indiscriminately tracking Belgians who were not members of the site, but whose activity was being logged using cookies and the “like” or “share” buttons on third-party sites.

Facebook won an appeal against the order on the basis that its European headquarters were in Dublin and therefore Belgium had no jurisdiction to regulate the social network.

Since then, the company has been fined €110m by the European commission for providing misleading information about the data-sharing possibilities between Facebook and WhatsApp, the messaging app it acquired in 2014.

European countries, including the UK, ordered the company to stop sharing WhatsApp user data, such as phone numbers, with the wider Facebook ecosystem.

Facebook is also facing scrutiny over WhatsApp from the EU data protection taskforce, Article 29 Working party, before the bloc’s tough new General Data Protection Regulations come into force in May.

Under the regulations, authorities will be able to fine firms such as Facebook up to 4% of their global turnover, or €20m.

The company recently began booking advertising revenue in the countries in which it is earned, rather than re-routing it through Ireland, under increasing political pressure. It paid just £5.1m in corporation tax last year in the UK, despite revenues quadrupling to £842.4m for the year to 31 December.

Facebook was among those recently told by the EU to do more and faster to remove extremist and hate content from its platform, or face regulation. It is under pressure from the British government over its carriage of Russian-backed ads during the Brexit referendum and its failure to stop the spread of fake news.