On 29 February 2024, Advocate General Emiliou of the Court of Justice of the European Union gave his Opinion in Belgian Association of Tax Lawyers and Others v. Premier ministre/Eerste Minister (Case C-623/22) on the compatibility of DAC6 with the principles of equality and non-discrimination, legality in criminal matters, legal certainty and the right to respect for private life. This contribution summarizes and criticizes the main elements of the Opinion, which will have major ramifications for the European tax transparency and tax cooperation regime if upheld by the Court of Justice of the European Union in its forthcoming DAC6 decision.