Since the annulment of Safe Harbor by the ECJ (C‑362/14) in October 2015, Facebook based its transatlantic data transfers on the EU standard contractual clauses. On May 25, 2016, the Irish Data Protection Authority (DPC) announced that it would have the legality of the standard contractual clauses as the basis for transatlantic data transfers assessed by the ECJ. Accordingly, the DPC initiated the proceedings Schrems against Facebook to the next instance, the Irish High Court. You will find our entry in this regard here.
According to Schrems the U.S. government today (June 13, 2016) asked the Irish High Court to participate in the proceedings. It is understood that the U.S. intends to defend its mass surveillance under PRISM in the European courts. The corresponding press release can be found here.