The principle of non-retroactivity, which is a general principle of EU law and is expressly referred to in Article 49 of the EU Charter on Fundamental Rights, applies to the Commission’s decisions imposing fines for breach of competition law. This principle requires that the penalties imposed on an undertaking for an infringement correspond with those laid down at the time when the infringement was committed. By contrast, it does not prevent the application of new guidelines including a new method of calculating fines which has an aggravating effect, when their adoption is foreseeable by the undertakings.