"We therefore think that the 'class action' is not only legal but also the only reasonable way to deal with thousands of identical privacy violations by Facebook."
Facebook, whose international headquarters are in Ireland, has denied any wrongdoing and sought to block a class action suit.
Ireland's High Court last month ordered an investigation into Facebook's transfer of European Union users' data to the United States to make sure personal privacy was properly protected from U.S. government surveillance.
The court told the Irish Data Protection Commissioner to launch a probe following the landmark ruling by the European Court of Justice last month which invalidated a pact, calle the Safe Harbour agreement, allowing thousands of companies to transfer user data from the continent to the U.S.
Under EU law, companies may not transfer personal data to countries deemed to have lower privacy standards, such as the U.S., unless they have legal contracts in place or have the explicit permission of the person in question.
Al Jazeera and Reuters