The constitutional character of the Union legal order based on the rule of law requires that secondary sources of Union law are not infringing the primary sources, including the Charter of the Fundamental Rights of the European Union (CFR). The latter’s importance as a valid instrument to be invoked against measures that are excessive in their interference with the fundamental rights has recently been reinforced by the Court of Justice of the European Union (CJEU) in the judgments in cases such as C-694/20, Orde van Vlaamse Balies and Others, and joined cases C-37/20 and C-601/20, Luxembourg Business Registers and Sovim. The CJEU invalidated provisions of the Directive on Administrative Cooperation (DAC6) and 5AMLD which reminded that this is the case even when rules are motivated by important collective interests. These include the combat against tax evasion and tax fraud and enhancing broadly understood transparency and are agreed upon and are ‘validated’ by a Union’s legislature. The lessons to be learned are not to be underestimated. Understanding where the limits lie is decisive for valid law making and law enforcement as well as for effectively invoking the rights of individuals and businesses.