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For many European Union scholars, the term ‘pre-emption’, when is not used in connection with a priori exclusive competences, immediately brings to mind the European Court of Justice (‘ECJ’) holding in ERTA that "each time the [Union] . . . adopts provisions laying down common rules . . . the Member States no longer have the right, acting individually or even collectively, to undertake obligations with third countries which affect those rules." The doctrine of pre-emption in the external sphere—that is, the limitations that the exercise of EU internal competences imposes on Member States’ power to undertake international commitments—is, possibly, the subject that has drawn most attention in the EU external relations law academic circles.
In contrast, legal scholarship has hitherto paid somewhat less attention to the doctrine of pre-emption in the internal sphere–that is, the restraints that the enactment of EU legislation imposes on national law-making powers. Its first application by the ECJ, which can possibly be traced back to the Unger ruling of 1964, went largely unnoticed by legal commentators of that time. Moreover, the ECJ hardly ever referred to this legal phenomenon by the term ‘pre-emption’ or its derivatives. Although in the early 1980s legal scholarship recognized pre-emption, along with direct effect and supremacy, as one of the hallmarks of Community normative supranationalism, no more than a handful of comprehensive treatments have been devoted to that subject since then.
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