According to the established case law of the Court of Justice, when national authorities or courts apply the European competition rules, the procedure is in principle governed by the domestic procedural rules by virtue of the principle of procedural autonomy. According to this principle, in the absence of European harmonization, it is up to the domestic legal system of each Member State to regulate the procedural arrangements for legal proceedings intended to safeguard the rights that individuals derive from the direct effect of European law. Therefore, domestic competition authorities are not bound by the methods of calculating fines used by the Commission in its guidelines. The principle of procedural autonomy can only be defeated if its implementation makes the application of European law impossible or excessively difficult.