Mo. Rev. Stat. § 70.620: Prior plan, effect of — discrimination between employees prohibited.

In the event an employer has in effect for all or part of its employees a plan similar in purpose to this system, by agreement with the board, after the board has received the advice of its technical advisors concerning such agreement, that employer may provide for coverage under this system of either some part or all of such employee's employment previously covered or coverable by such other plan, provided such coverage and resulting benefits hereunder do not duplicate any benefits previously provided by such other plan. In providing for such coverage, an employer and the board shall pursue uniform policies and shall not discriminate in favor of or against any such employee or group of such employees.