La. Revenue and Taxation § 47:338.37
When any bonds shall have been issued hereunder, neither the Legislature of Louisiana nor the municipality may discontinue or decrease the tax or permit same to be discontinued or decreased in anticipation of the collection of which such bonds have been issued, or in any way make any change in the allocation of the proceeds of such tax which would diminish the amount of the sales tax revenues to be received by the governing authority, until all of such bonds shall have been retired as to principal and interest, and there is hereby vested in the holders from time to time of such bonds and the coupons representing interest thereon a contract right in the provisions of this Section and of R.S. 47:338.30 through 338.47.
La. Revenue and Taxation § 47:338.37