Contractual arbitration (arbitrato irrituale) is contractual in nature and constitutes an expression of the parties' contractual autonomy, whereby the parties confer upon the arbitrators a joint mandate for the settlement of the dispute by means of an act having the nature of a contract, rather than of a jurisdictional pronouncement.
A breach of the adversarial principle in contractual arbitration (arbitrato irrituale), relevant pursuant to Article 808-ter of the Code of Civil Procedure, occurs when the arbitrators fail to guarantee the parties the opportunity to address every fundamental point of the dispute, omitting to disclose the results of the evidentiary proceedings, to allow replies to the opposing defences, or to permit discussion on factual aspects relevant to the decision.
Compliance with the adversarial principle in contractual arbitration (arbitrato irrituale) does not require the arbitrators to admit any evidentiary request made by the parties, since the means of proof must meet the requirements of admissibility and relevance, the assessment of which is entrusted to the prudent discretion of the arbitrators, who must balance the need to avoid superfluous procedural activities with that of ensuring the conclusion of the proceedings within a reasonable time.
The refusal by the arbitral tribunal to admit witness evidence does not constitute a breach of the adversarial principle when such decision is supported by adequate reasoning as to the superfluity of the requested evidentiary means, by reason of the sufficiency of the evidentiary elements already acquired in the proceedings.