Tex. Gov't Code § 845.507

It is intended that this subtitle be construed and administered in a manner that the retirement system will be considered qualified under Section 401(a) of the Internal Revenue Code of 1986 (26 U.S.C. Section 401). The board of trustees may adopt rules that it determines necessary for the retirement system to be considered qualified. Rules adopted by the board of trustees relating to qualification issues are considered a part of the plan.