see this article in the full MAL
article 16. Competence of arbitral tribunal to rule on its jurisdiction
(2) A plea that the arbitral tribunal does not have jurisdiction shall be raised not later than the submission of the statement of defence. A party is not precluded from raising such a plea by the fact that he has appointed, or participated in the appointment of, an arbitrator. A plea that the arbitral tribunal is exceeding the scope of its authority shall be raised as soon as the matter alleged to be beyond the scope of its authority is raised during the arbitral proceedings. The arbitral tribunal may, in either case, admit a later plea if it considers the delay justified.
SEE ALSO THE SEPARATE ENTRIES FOR THE OTHER SECTIONS OF THIS ARTICLE.