A plea that the arbitral tribunal does not have jurisdiction shall be raised not later than the submission of the statement of defense. However, a party is not precluded from raising such a plea by the fact that he or she has appointed, or participated in the appointment of, an arbitrator.
Source:
Section 1297.162, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CCP§ionNum=1297.162..