In the wake of the accession of new EU Member States in 2004 and in 2007, the portfolio of bilateral investment treaties (BIT) between Member States has become significantly larger. The fact that these BITs overlap with EU law creates friction when BITs are applied by investment tribunals which are constituted thereunder. In the spirit of the requirement that EU law be applied uniformly, these tribunals should have the authority to refer matters to the ECJ for preliminary rulings. Given the peculiarities of commercial and investment arbitration tribunals, it will not do to point to the previous case law of the ECJ on the admissibility of requests for a preliminary ruling by international commercial tribunals (i.e., in particular, Nordsee, Danfoss). In assessing the options of investment arbitration tribunals for referring matters for a preliminary ruling, one must put the focus on the basis of their jurisdiction, which derives from the provisions of the given legal system, i.e., the international treaty.