Between 2008 and 2015 a dozen of the European constitutional courts, as well as the UE Court of Justice, assessed legal provisions on data retention. Judiciary on this pan-European mass-surveillance measure poses a unique research opportunity. We argue that ad hoc confederation of constitutional courts within the EU has been established despite lack of regulations enforcing such cooperation. It was caused by the introduction of a legal mechanism interfering with fundamental rights, specificity of the EU legal order which resembles a system of connected vessels and one common legal problem of a major social significance. On the basis of this unique maze of judgments, we identified three cooperation models that those constitutional courts took. The keystone of those models was their approach towards the European Court of Human Rights and the Court of Justice of the European Union. In our presentation, we will discuss how this unique dialogue of courts proceeded and what its effects were.