The question whether and to what extent procedural guarantees under criminal law must be respected in EU and German antitrust enforcement has not been completely clarified yet. It is a current and fundamental problem as it influences the specific design of the powers of investigation and sanction of the Commission and national authorities enforcing Articles 101 and 102 TFEU. After examining the level of protection of fundamental rights, with a particular focus on the decentralized application of EU competition law, the author analyses the legal nature of the respective competition proceedings. On the basis of the previous findings, he defines the limits of investigative powers using the example of the nemo tenetur principle. In particular, the author verifies whether the power to request information pursuant to Article 81a Act Against Restraints of Competition (ARC), which was incorporated into law with the 8th amendment to the ARC, is compatible with the nemo tenetur principle.