The nullity of the substantive contract does not automatically entail the invalidity of the arbitration clause contained therein, which, by virtue of the principle of separability enshrined in Article 808 of the Code of Civil Procedure, constitutes a distinct and separate juridical act. The validity of the clause must be assessed independently of the main contract, thereby enabling the arbitrators to maintain their jurisdiction even when they find the contractual relationship from which the dispute arises to be null and void.
The arbitral tribunal, having affirmed its jurisdiction by virtue of the validity of the arbitration clause, is entitled to find and declare the nullity of the substantive contract for breach of mandatory rules, including those concerning public procurement, without such a declaration retroactively affecting the power to adjudicate already validly acquired.
Arbitrators, exercising the powers of an ordinary court by virtue of the arbitration clause, may exercise the power to disapply unlawful administrative acts where the question of their lawfulness arises incidentally as a necessary logical antecedent for the determination of the dispute concerning subjective rights arising from the contractual relationship, provided that this does not amount to a review of the discretionary assessments of the public authority.
A challenge to an arbitral award constitutes proceedings subject to limited grounds of review, available exclusively on the grounds of nullity exhaustively prescribed by law, requiring the specific identification of the parts of the award challenged and a precise statement of the violations alleged.