Under CCP 1281.91(b), a party has an absolute right to disqualify a neutral arbitrator (once) without cause if done within 15 days of the arbitrator’s providing the parties the disclosures required by CCP 1281.9.  This decision holds that the right to peremptorily disqualify a neutral arbitrator under section 1281.91 is not waivable in advance so that defendant could disqualify the arbitrator, who had presided over an earlier arbitration between the parties, from hearing a new arbitration between the same parties, even though the parties had agreed before the first arbitration that the arbitrator would handle any and all arbitrations between them.