The harmonisation of the internal market is a fundamental aspect of the EU acquis, and the Digital Markets Act (DMA) is no exception. It aims to harmonise digital markets across the Union on the basis of the concepts of contestability and fairness. The DMA is enforced through a quasi-centralised enforcement system, with the European Commission as its sole enforcer and national competition authorities (NCAs) playing a secondary and supporting role in monitoring. The EC’s centralisation of enforcement powers is key to ensuring harmonisation. This paper highlights the potential risks at the national level due to NCA involvement in the enforcement and monitoring of the DMA. While the Regulation does not need to be transposed into national law to be effective, some Member States have introduced legislation specifying which authorities are responsible for enforcement and how they should apply their powers in line with the DMA. The paper examines these legislative developments, revealing potential deviations that undermine the effective enforcement of the DMA and disrupting its current centralised enforcement system.