Facebook has endured mounting problems in Europe recently; the social network is facing court cases in several EU countries, with most of the accusations against the company revolving around its privacy and tracking policies. It now faces more complications in Germany, where the country's highest court has declared the site's 'friend finder' feature unlawful.

A panel of the Federal Court of Justice ruled that the promotional feature constituted advertising harassment in a case that was filed in 2010 by the Federation of German Consumer Organisations (VZBV).

Friend Finder requests users' permission to access the email addresses of contacts in their address book so invitations can be sent to non-Facebook members asking them to join the service.

The court said this was a deceptive marketing practice, confirming two lower Berlin courts' decisions in 2012 and 2014, which had found that Facebook had violated German laws on data protection and unfair trade practices. The company was also accused by the court of not adequately informing members about how it was using their contacts' data.

"Invitation emails from Facebook to people who have not clearly consented to receiving them are an unacceptable nuisance," the court said in its ruling.

A spokeswoman for Facebook said the company would be looking into the ruling as soon as it is available in full. "We will study it carefully to assess any impact on our services today," she said.

The VZBV welcomed the decision and said in a statement that it will have implications for other companies in Germany that use similar forms of promotional advertising to attract new users.

"What the judgment means exactly for the current Friends Finder, we now have to find out," said Klaus Mueller, head of the VZBV.