Article 81(1) of the EC Treaty prohibits "all agreements between undertakings, decisions by associations of undertakings and concerted practices which may affect trade between Member States and which have as their object or effect the prevention, restriction or distortion of competition within the common market". Article 81(1) provides a non-exhaustive list of practices caught by the above provision that includes:
Article 81(2) provides that any agreements or decisions prohibited pursuant to article 81(1) shall be automatically void and unenforceable without the need for any act or finding of the European Commission (the 'Commission') or any other enforcement agency or court.
Please note bolded.
Be well