This note examines the ECJ preliminary ruling issued on 8 June 2023 in E. v. Dyrektor Izby Administracji Skarbowej we Wrocławiu (The Tax Chamber in Wrocław) (Case C-322/22), which challenges the EU law compatibility of Polish regulations that impose restrictions on the payment of interest on overpaid taxes based on the timing of refund requests. The ECJ emphasized the importance of the principles of effectiveness and sincere cooperation in ensuring that taxpayers receive adequate compensation for unlawfully levied taxes, including the payment of interest.