Miss. Code § 25-11-421
The Board of Trustees of the Public Employees' Retirement System shall determine whether the optional retirement program shall be operated in conformity with Section 403(b) of the Internal Revenue Code or be qualified under Section 401(a) of the Internal Revenue Code (or any successor section). If the optional retirement program is to be qualified, the board of trustees shall file for a determination letter from the Internal Revenue Service as soon as practicable, and not later than ninety (90) days, after this article has been approved by the Governor or has been approved by the Legislature subsequent to veto, and the continuance of the optional retirement program shall be subject to a favorable determination letter issued by the Internal Revenue Service.
Miss. Code § 25-11-421