The Belgian Constitutional Court on 17 December 2020 issued its decision in a case challenging the constitutionality of the Flemish decree transposing the sixth iteration of the EU Directive on administrative cooperation in tax matters (DAC6). DAC6 requires intermediaries to report tax planning arrangements falling under specified hallmarks. An intermediary who is prevented from reporting due to legal professional privilege is required to notify other intermediaries, if any, and the relevant …