The case concerns the compatibility of national rules on the retroactive application of more lenient criminal laws (lex mitior) in VAT fraud cases with the obligations under Article 325 TFEU and the PIF Convention. The referring court asks whether a conspiracy to commit VAT fraud can already constitute a breach of the EU’s financial interests, and whether national rules preventing the interruption of limitation periods, based on constitutional principles like the prohibition of lex tertia, must be set aside to ensure effective enforcement of EU financial crime law, even when fundamental rights under the Charter and the ECHR are at stake.