The Italian govt had levied a tax on P in breach of EC law, but claimed that the time limit, which it had retroactively imposed without a transitional period, for a reimbursement claim under domestic law had passed. ECJ held that where no adequate transitional period is provided during which claims relating to sums paid before the entry into force of the legislation introducing the new time-limit may still be brought within the old period. This contradicts the principle of effectiveness.
ECJ: In the absence of community rules on the matter it is for domestic law to set out rules of procedure, jurisdiction of domestic courts etc that relate to the enforcement of EC laws, provided that the principles or effectiveness/practical possibility and equivalence are upheld. This was not the case here where effectiveness was precluded by the operation of the retroactive time limit without a transitional period.