Proceedings for setting aside an arbitral award on grounds of nullity are subject to the rule of restricted grounds of challenge and may be brought only for specific errors of procedure expressly provided for by Article 829 of the Code of Civil Procedure; a review of the merits of the dispute is not the primary object of the rescinding phase and may be undertaken only contingently, upon a positive finding as to the ground of nullity invoked.
An arbitral award is null and void, for violation of the right to be heard and the right of defence under Article 829, paragraph 1, No. 9, of the Code of Civil Procedure, where the decision is founded on a point of law raised by the arbitral tribunal on its own motion only at the decision-making stage and never submitted to the parties for argument in the course of the proceedings (the so-called third-way decision).