California Code, Revenue and Taxation Code - RTC § 7270

(a) Prior to the operative date of any ordinance imposing a transactions and use tax pursuant to this part, the district shall contract with the board to perform all functions incident to the administration and operation of the ordinance. If the district has not contracted with the board prior to the operative date of its ordinance, it shall nevertheless so contract and, in that case, the operative date shall be the first day of the first calendar quarter following the execution of the contract.

(b) The contract shall contain a provision that the district shall reimburse the board for and hold the board harmless from any and all costs, losses, or refunds of any kind whatsoever.

(c) The contract shall also contain a provision that, in the event that a legal action is commenced challenging the validity of the tax in its entirety, as opposed to its application to an individual taxpayer, the district shall place the tax proceeds into an interest-bearing escrow account until the legality of the tax is finally resolved by a final and nonappealable decision rendered by a court of competent jurisdiction. That provision shall be enforceable by any interested person in a proceeding for a writ of mandate.

(d) The district shall be entitled to indemnity for any and all costs, losses, or refunds from any entity, except the state, that participated in the imposition of the tax. For the purposes of this part, “participated” means any involvement in procuring the legislation that authorized the tax, or in enacting or administering the ordinance imposing the tax. Any organization that is a member of the legislative body of the district imposing the tax has participated in the imposition of the tax within the meaning of this section.