Great interest is given to the application of the principle non bis in idem according to the European Convention on Human Rights and the European Court of Human Rights’ case law in tax matters these days. This case law is concurrently assumed also by the Court of Justice of the European Union when the European Union law is implemented. However, this case law is affected by the significant change resulting from the unwillingness of member states to accept the previous interpretation of the European Convention on Human Rights in tax matters established by the decision in the so-called A and B case. Therefore, the Court of Justice of the European Union faces the decision whether the current state of the interpretation of the non bis in idem principle resulting from the European Court of Human Rights’ case law should be preserved or if this court should establish own and broader union concept of non bis in idem principle. In the conclusion, the author provides his own opinion on which approach should be chosen with the aim to maintain the legal certainty of the recipients of law.