A contractual arbitration award (arbitrato irrituale), being contractual in nature, may be challenged exclusively on grounds of defects that may vitiate any contractual manifestation of will, such as incapacity of the parties or arbitrators, defects of consent, and excess of mandate, whilst errors of judgment concerning the assessment or interpretation of law remain irrelevant, being incompatible with the contractual nature of the award itself.
In contractual arbitration (arbitrato irrituale), arbitrators authorised to decide ex aequo et bono do not incur the defect of excess of mandate where they apply the law, if they find that law and equity coincide, such coincidence being capable of being inferred implicitly from the body of reasoning put forward in support of the decision, the defect arising only where the arbitrators deny a priori the possibility of availing themselves of the equitable powers conferred upon them.
In matters of corporate arbitration, Article 36 of Legislative Decree No. 5/2003, where applicable ratione temporis, requires arbitrators to decide according to law even in the presence of an arbitration clause authorising a decision ex aequo et bono, with the consequent admissibility of challenge to the award for breach of the substantive rules of law governing the merits of the dispute.
A challenge to a contractual arbitration award (arbitrato irrituale) cannot be founded on grounds of nullity of the arbitration clause that were not raised during the arbitration proceedings.