Cal. Gov. Code § 3548
Either a public school employer or the exclusive representative may declare that an impasse has been reached between the parties in negotiations over matters within the scope of representation and may request the board to appoint a mediator for the purpose of assisting them in reconciling their differences and resolving the controversy on terms which are mutually acceptable. If the board determines that an impasse exists, it shall, in no event later than five working days after the receipt of a request, appoint a mediator in accordance with such rules as it shall prescribe. The mediator shall meet forthwith with the parties or their representatives, either jointly or separately, and shall take such other steps as he may deem appropriate in order to persuade the parties to resolve their differences and effect a mutually acceptable agreement. The services of the mediator, including any per diem fees, and actual and necessary travel and subsistence expenses, shall be provided by the board without cost to the parties. Nothing in this section shall be construed to prevent the parties from mutually agreeing upon their own mediation procedure and in the event of such agreement, the board shall not appoint its own mediator, unless failure to do so would be inconsistent with the policies of this chapter. If the parties agree upon their own mediation procedure, the cost of the services of any appointed mediator, unless appointed by the board, including any per diem fees, and actual and necessary travel and subsistence expenses, shall be borne equally by the parties.
Ca. Gov. Code § 3548