The objection that the dispute should be referred to arbitration, based on an arbitration clause, constitutes a defence in the strict sense having as its object the assertion of a fact precluding the exercise of State jurisdiction, being characterised as a waiver of the right to bring judicial proceedings through an instrument of a private-law nature; being a question on the merits concerning the interpretation and validity of the submission to arbitration or the arbitration clause, it must be raised within the time and in the manner prescribed for defences on the merits.