The complaints against Apple and Facebook were made in Ireland, while the complaints filed in Luxembourg focused on Microsoft and Skype. The complaint against Yahoo was filed in Germany. Each of these U.S. companies have European divisions that must follow the privacy laws of the continent even if the data is processed by the U.S. subsidiary of each firm.
If a European subsidiary sends user data to the U.S.parent, this export of data is allowed only if the European division can guarantee "adequate protection" in the foreign country. Since this cannot be promised in light of the NSA PRISM disclosure, the European subsidiaries of the named companies are committing an illegal act.
These same European subsidiaries are required by European law to answer questions about their involvement in PRISM. The Europe v Facebook group says that the European divisions of these companies can either show some proof that they are not involved in the scandal, or explain why the gathering of information by the NSA fits into European data protection laws.
source: EuropevFacebook via BGR