German data protection authorities Tuesday ordered Facebook to delete data, such as phone numbers, it has received from its subsidiary WhatsApp.
Facebook acquired the global messaging service two years ago and announced this summer that WhatsApp would begin sharing the phone numbers of its users with the social network as part of a program to synchronize the two businesses.
But Hamburg's Commissioner for Data Protection ruled that Facebook "neither has obtained an effective approval from the WhatsApp users, nor does a legal basis for the data reception exist."
"After the acquisition of WhatsApp by Facebook two years ago, both parties have publicly assured that data will not be shared between them," the agency said in a statement. "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."
Facebook, whose German operations are based in Hamburg, questioned the ruling.
"Facebook complies with EU data protection law," the company said in an email to The Associated Press. "We will work with the Hamburg DPA in an effort to address their questions and resolve any concerns."
The California-based company has faced repeated challenges in Germany, where there are strict laws on data privacy and intellectual property.
In March, the country's competition watchdog said it was investigating whether Facebook used its dominant market position to make users give too much personal information. Facebook rejected any claim of wrongdoing and said it would work with the Federal Cartel Office to answer their questions.
The month before that, Facebook was fined 100,000 euros ($112,000) by a Berlin court for failing to narrow down what rights Facebook has to use the photos and videos of users.