France's Commission Nationale de L'Informatique et des Libertés, otherwise known as CNIL, has given social media giant Facebook a deadline of three months by which it must stop tracking users who are not signed up members.
If not, CNIL is threatening to hit Facebook with fines.
CNIL says Facebook is following browsing activity after people visit a publicly viewable Facebook page from the site, even if they don't have a Facebook account.
The watchdog also says Facebook sets up cookies that pass on more information when users without accounts visit other sites that use Facebook plugins.
CNIL is also not happy with Facebook apparently storing information about users' sexual orientation as well as religious and political views, without their consent.
Plus CNIL says Facebook violated users' right to privacy by gathering data on their habits for advertising purposes.
CNIL has invoked an order in October last year by the Court of Justice of the European Union, which declared invalid a "safe harbour" agreement governing personal data transfers between the European Union and the US.
The US and the EU this month agreed on an arrangement, called the EU-US Privacy Shield, which aims to replace the "safe harbour" but it is not currently operational.
According to CNIL, Facebook has more than 30 million users in France.
The authority went public with its deadline to the company “due to the seriousness of the violations and the number of individuals concerned by the Facebook service.”
Sally Aldous, a spokeswoman for Facebook, told Bloomberg news: “Protecting the privacy of the people who use Facebook is at the heart of everything we do. We are confident that we comply with European Data Protection law and look forward to engaging with the CNIL to respond to their concerns.”