Texas Government Code - GOV'T § 845.102. Rules and Standards

(a) The board of trustees shall adopt rules and perform reasonable activities necessary or desirable for efficient administration of the system.

(b) Subject to the provisions of this subtitle, the board of trustees may establish systemwide standards to which all subdivisions are subject and that apply to all members of the retirement system or to all members similarly situated in a class.  The board may establish or modify a systemwide standard at a time and in a manner the board determines to be appropriate and in the best interests of the system, the members, or their beneficiaries.