By virtue of Article 49 of the EU Charter on Fundamental Rights no one shall be held guilty of any criminal offense on account of any act or omission which did not constitute a criminal offense under national law or international law at the time when it was committed and a heavier penalty  than the one that was applicable at the time the criminal offense was committed cannot be imposed. The Commission’s power to impose penalties for the infringement of Articles 101 and 102 TFEU is in line with that principle.

The principle that offenses and punishments must have a legal basis gives rise to two corollary principles: legal certainty, which means that the Commission is precluded from calling into question in an unpredictable manner positions already acquired, and the protection of legitimate expectations, which can be invoked the principle of the protection of legitimate expectations, which can be invoked by undertakings in respect of which an institution has created reasonable expectations by providing them with specific assurances. Often relied upon by undertakings, the applicability of those principles is very rarely accepted by the EU courts.