The European Union responded to the propositions of the OECD in the BEPS Action 12 Final Report on Mandatory Disclosure Rules (MDR) by creating its own rules in the form of Council Directive 2018/822 of 25 May 2018, which is the sixth amendment of Directive 2011/16/EU on administrative cooperation in the field of taxation (DAC 6). This article focuses on the controversial aspects of DAC 6, namely its impact on the fundamental rights of taxpayers. It investigates (i) how the European MDR indirectly affect the taxpayers’ right to legal certainty and legitimate expectations through active prevention of “aggressive” or “potentially aggressive” tax schemes by rapid changes in legislation; (ii) how they will impact the taxpayers’ right to legal advice and legal representation, as well as the right not to self-incriminate; and (iii) what the interplay is between taxpayers’ right to privacy and data protection and the reporting requirements.