German data protection authorities have ordered Facebook to delete data - including phone numbers - the social media giant 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 within the network as part of a plan to synchronise the two businesses.
However, Hamburg's commissioner for data protection ruled Facebook "neither has obtained an effective approval from the WhatsApp users, nor does a legal basis for the data reception exist".
Facebook, whose German operations are based in Hamburg, did not immediately respond to a request for comment.
The California-based company has faced repeated challenges in Germany, where there are strict laws on data privacy and intellectual property.