Ind. Code § 6-9-33-9
(b) With respect to obligations for which a pledge has been made under this section before January 1, 2009, the general assembly covenants with the holders of these obligations that:
(2) this chapter will not be amended in any manner that will change the purpose for which revenues from the tax imposed under this chapter may be used;
as long as the payment of any of those obligations is outstanding.
As added by P.L.8-2000, SEC.3. Amended by P.L.176-2009, SEC.19.