The privacy investigation is as a result of German privacy watchdogs over the facial recoginition technology that Facebook uses.
The Photo Tag Suggest feature encourages individuals to share photographs posted to Facebook and tagged by users.
German authorities have objected to the technology due to the opt-out basis ensuring every user is part of the new system, unless they opt out.
However, regardless of the ability to opt out the facial recognition software has already managed to create a database of each individuals biometric profiles.
Facebook did agree to suspend the service in July whilst it discussed the system with regulators. However, a formal investigation has now been re-opened. This could mean that Facebook may face a fine or even a possible court case which could result in Facebook having to make changes to its system if it loses.
An audit is underway that will produce a conclusion in the next few months.