(a) Any governmental entity of this state may:
(1) use and pledge available revenue for the payment of an amount due under a contract entered into with the authority as an additional source of payment of the contracts or as the sole source of payment of the contracts; and
(2) covenant with respect to available revenue to assure the availability of the revenue when required.
(b) The governmental entity may not use, pledge, or covenant under this section revenue from ad valorem taxes, or the proceeds of bonds paid wholly or partly from ad valorem taxes, unless the use, pledge, or covenant has been approved by the voters of the governmental entity at an election called for the purpose of:
(1) imposing taxes or issuing or refunding bonds; or
(2) using or pledging the entity's revenue or proceeds under contracts with the authority under this chapter.