On 30 May 2013 the European Court of Justice ("ECJ") upheld the judgement of the General Court ("GC") in the case Quinn Barlo and Others v. Commission (C-70/12 P). The ECJ affirmed the compatibility of the GC's judgement with the general principles of European Union ("EU") law, including the presumption of innocence, the protection of legitimate expectations, and equal treatment.

The Appellants had been found by the Commission to have infringed Article 101 TFEU by engaging on a series of price agreements and exchanging of commercially sensitive information for the polymethyl-methacrylate market. On appeal, the GC concluded that the infringement was of shorter duration than that found by the Commission, namely 11 months and 28 days. The GC thus reduced the fine by 10%. In addition, the original increase in the fine for cartel length was reduced from 20% to 10%. Notwithstanding that according to the 1998 Fining Guidelines, infringements of less than one year do not merit any increase in the fine, the GC stated that it sought to reflect the duration of the participation. The GC held that the Guidelines do not set out provisions as imperative rules and cannot bind the court.

Before the ECJ, the Appellants claimed that the GC did not follow the 1998 Guidelines in calculating the fine and had therefore committed an error. The ECJ, however, upheld the GC's judgement in full. The ECJ reaffirmed that the GC is entitled in its "exercise of unlimited jurisdiction" to substitute its own appraisal for the Commission's in relation to the fines. The Guidelines are self-imposed restrictions by the Commission, however, they cannot bind the Courts of the Union. The Courts may depart from these guidelines and state their reasons. In the present case, the Appellants failed to challenge the reasoning of the GC and thus their appeal in this respect failed. The ECJ reaffirmed that the courts will "consider case by case situations before them, taking into account all the matters of fact and law relating to them".