Facebook has been ordered to delete all the data that it currently holds of Germany’s 35 million WhatsApp users.

Johannes Caspar, the data protection commissioner of Hamburg, where Facebook Germany is headquartered, said Tuesday there was no legal basis for Facebook to use WhatsApp's user information.

“Facebook and WhatsApp are independent companies that process their user's data on the basis of their own terms and conditions and data privacy policies. After the acquisition of WhatsApp by Facebook two years ago, both parties have publicly assured that data will not be shared between them. The fact that this is now happening is not only a misleading of their users and the public, but also constitutes an infringement of national data protection law,” said Caspar in a statement, adding that “It has to be [users’] decision as to whether they want to connect their account with Facebook. Therefore, Facebook has to ask for their permission in advance. This has not happened.”

Facebook’s European headquarters are in Ireland and the company has repeatedly refused to recognise other jurisdictions in multiple privacy cases, but it also operates a subsidiary in Hamburg for the operation of marketing in German-speaking regions.

When the companies merged in 2014, WhatsApp pledged not to share users’ data—but in a U-turn last month the company revealed it would in fact be sharing information with Facebook.

Caspar is also concerned about Internet users whose contact details were uploaded to WhatsApp from a friend’s address book, even though they have no accounts with Facebook or WhatsApp themselves. “According to Facebook, this gigantic amount of data has not yet been collected. Facebook’s answer, that this has merely not been done for the time being, is cause for concern that the gravity of the data protection breach will have much a more severe impact,” he said.

In a statement Facebook said it would appeal the order: “Facebook complies with EU data protection law. We will appeal this order and we will work with the Hamburg DPA in an effort to address their questions and resolve any concerns."

Earlier this month, the Federation of German Consumer Organisations (VZBV) threatened legal action against WhatsApp for passing on user information to Facebook. “We are extremely concerned about this insidious trend: consumers are losing step by step the ownership of their data. Their private sphere is in danger,” it said. As WhatsApp failed to sign a “cease and desist letter” by September 21, legal action now seems inevitable.

In the US, the Federal Trade Commission has also received complaints from The Electronic Privacy Information Center (EPIC), and the Center for Digital Democracy over the issue.

A joint meeting of all Europe’s data protection authorities this week will also examine the situation.