When the messaging service WhatsApp announced last month that it was starting to share some of its users’ online information with Facebook, its parent company, many users expressed anger that their digital privacy could be at risk.

Now, a German regulator thinks so, too.

The city of Hamburg’s data protection commissioner ordered Facebook on Tuesday to stop collecting and storing data on WhatsApp users in Germany, the first time a privacy watchdog has waded into the debate. The regulator also called on the social network to delete all information already forwarded from WhatsApp on roughly 35 million German users.

“It has to be their decision, whether they want to connect their account with Facebook,” Johannes Caspar, the Hamburg data protection commissioner, said in a statement. “Therefore, Facebook has to ask for their permission in advance. This has not happened.”