More than a year ago, a Polish regional court referred two questions to the European Court of Justice (ECJ) on the conformity with Community law of the provision of the Polish VAT Law under which a 30% charge is imposed on taxable persons who have understated their output VAT liability or overstated their input VAT claim in their VAT return. That charge has legally been labelled as an "additional tax liability" and is imposed on taxable persons who have made a mistake in their VAT return. In this article, the authors explain the background of the preliminary questions.