The paper critically examines the impact of the hierarchy of norms within the EU legal order, and its interaction with the pre-emption principle, on the constitutional function of the Court of Justice. The emphasis is placed on the limits set by the primacy of the Treaties to the pre-emptory effect of secondary EU law in fields of the internal market, which have been harmonised. The standards applied to the fundamental freedoms are contrasted to the Court’s approach to the tax law area. The paper questions whether the latter may be evidence of a tax exceptionalism. It is suggested that if this is the case, the Court of Justice should abandon its exceptional approach to the field of taxation and align its standards with the ones applied to other internal market policy areas which have been subject to EU harmonisation measures, such as the free movement provisions.