Tex. Local Government Code § 271.095

(a) The local government may pledge payments to secure any obligation only if the amount of payments received by the local government in the fiscal year of the state preceding the proposed issuance equals or exceeds the amount required in each year to pay the sum of an amount equal to two times (i) the maximum annual principal and interest requirements for the obligation, and (ii) the maximum annual principal and interest requirements on any additional obligation for which payments have been pledged. The local government shall provide evidence that these requirements are met.

(b) A pledge of payments pursuant to this subchapter is a first priority for application of payments and the comptroller shall apply such payments as provided by this subchapter prior to applying such payments pursuant to any other authorization to withhold or intercept such payments.

(c) While obligations which are the subject of an agreement remain outstanding, the local government may not repeal the sales tax or reduce the rate of the sales tax below the rate that would provide the amount required by Subsection (a), except as provided by this subsection. If at an election duly held in accordance with law a majority of the qualified voters approve the repeal of the sales tax, the local government shall, at the earliest practicable time, refund or defease the obligations, and after such defeasance or refunding the repeal shall become effective in accordance with law. If the qualified voters vote to reduce the rate of the sales tax, if such is provided for by law, below that which is required to provide the amount required by Subsection (a), the local government shall, at the earliest practicable time, refund or defease the obligations, and after such defeasance or refunding the reduction in rate shall become effective in accordance with law.