All persons who become employees, as defined in R.S. 11:1002, on or after August 1, 1962, may become members of this system during the first ninety calendar days immediately following the date of employment, and shall become members on the ninety-first calendar day following the date of employment as a condition of their employment. All employees who were employed prior to August 1, 1962, shall be governed by and have the benefit of all existing applicable laws.
La. Consolidated Public Retirement § 11:1116