The contribution revolves around the story of the regulation that in 2008 introduced an IRES surtax charged to the oil industry (the so-called "Robin Hood tax") declared illegitimate by the Constitutional Court with a decision issued on 11 February 2015. In particular, the author analyzes the position of administrative case law that had ruled groundless the questions of constitutionality raised with regard to the new levy and the critical positions put forward by doctrine, then going on to thoroughly investigate the reasons on which the constitutional court based his ruling. A critical analysis of the line of reasoning used by the Constitutional Court, particularly in the part of the decision regulating the temporal effects of the declaration of unconstitutionality, leads the author to examine the content/- substantive value of the balanced-budget obligation provided under the new Art. 81 of the Constitution. The article stresses the crisis of sovereignty affecting the Parliament, which was incapable of regulating the market, crushed by the political attitude of the constitutional court and helpless before the regulatory strength of the supranational system.