Belgium's national privacy watchdog is taking US internet company Facebook to court, arguing that the way the social network website tracks the behaviour of both members and non-members is illegal under Belgian and European law.

“Facebook's behaviour is unacceptable”, Willem Debeuckelaere, president of Belgium's Commission for the protection of privacy, said.

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It is the first time a national privacy watchdog in Europe sues Facebook for not complying to privacy law.

The basis for the case is research requested by the privacy commission and published in March, which noted that Facebook tracks user behaviour on non-Facebook websites by default until they opt-out, instead of after seeking permission.

“As emphasised by the [European data protection body] Article 29 Working Party, an opt-out mechanism “is not an adequate mechanism to obtain average users informed consent”, particularly with regard to behavioural advertising. This means that Facebook’s current opt-out approach does not satisfy the requirements for legally valid consent”, the researchers concluded.

It also noted that Facebook tracks the behaviour of people who are not members of Facebook, which also violates the EU's e-Privacy directive.

“Even people who explicitly state that they do not want to be tracked, are tracked anyway”, Debeuckelaere told Belgian newspaper De Morgen, which broke the story on Monday (15 June).

Last month, the Belgian privacy commission presented its findings and recommendations to Facebook, whose European office is registered in Ireland.

“They answered that they do not accept Belgian law or the authoritiy of the Belgian privacy commission, and that it is all a misunderstanding”, said Debeuckelaere.

A Facebook spokesperson told this website in an e-mail the company is “confident that there is no merit” in the case by the privacy watchdog, known in Belgium by its acronym CBPL.

“We were surprised and disappointed that, after the CBPL had already agreed to meet with us on the 19th June to discuss their recommendations, they took the theatrical action of bringing Facebook Belgium to court on the day beforehand.”

A court in Brussels will hear the case on Thursday (18 June). Willem Debeuckelaere told this website in an e-mail the date for the hearing, one day before another CBPL-Facebook meeting, is a coincidence.

It is not the first time Facebook has come under fire over privacy in Europe. Austrian Facebook user Max Schrems has taken his case against Facebook all the way to the EU's Court of Justice. He announced last week an opinion by adocate general Yves Bot, which was scheduled for 24 June, has been delayed.

EU ministers, for their part, will Monday discuss setting up a European privacy watchdog.