Cal. Code of Civil Procedure § 1281.91

(a) A proposed neutral arbitrator shall be disqualified if he or she fails to comply with Section 1281.9 and any party entitled to receive the disclosure serves a notice of disqualification within 15 calendar days after the proposed nominee or appointee fails to comply with Section 1281.9. (b) (1) If the proposed neutral arbitrator complies with Section 1281.9, the proposed neutral arbitrator shall be disqualified on the basis of the disclosure statement after any party entitled to receive the disclosure serves a notice of disqualification within 15 calendar days after service of the disclosure statement. (2) A party shall have the right to disqualify one court-appointed arbitrator without cause in any single arbitration, and may petition the court to disqualify a subsequent appointee only upon a showing of cause. (c) The right of a party to disqualify a proposed neutral arbitrator pursuant to this section shall be waived if the party fails to serve the notice pursuant to the times set forth in this section, unless the proposed nominee or appointee makes a material omission or material misrepresentation in his or her disclosure. Except as provided in subdivision (d), in no event may a notice of disqualification be given after a hearing of any contested issue of fact relating to the merits of the claim or after any ruling by the arbitrator regarding any contested matter. Nothing in this subdivision shall limit the right of a party to vacate an award pursuant to Section 1286.2, or to disqualify an arbitrator pursuant to any other law or statute. (d) If any ground specified in Section 170.1 exists, a neutral arbitrator shall disqualify himself or herself upon the demand of any party made before the conclusion of the arbitration proceeding. However, this subdivision does not apply to arbitration proceedings conducted under a collective bargaining agreement between employers and employees or their respective representatives.