Sec. 1. No pension or retirement benefit plan or system for employees of any Texas municipality, whether provided for by general or special law, city charter, or city ordinance, shall become or be made applicable to employees of any Board of Trustees created or appointed in pursuance of Article 1115, Revised Statutes, or any similar law providing for a Board of Trustees to administer municipal utilities or properties, unless and until such pension or retirement benefit plan or system has been approved and adopted by the Board of Trustees employing such employees and such Board of Trustees has made provision for the payment out of the revenues of the utility systems or its properties of the necessary payments to be made as the employer’s contribution to such pension or retirement benefit plan or system.

Sec. 2. Any plan or system providing for pensions or retirement benefits which may have heretofore been adopted or may hereafter be adopted by any such Board of Trustees may be applied to the employees of such Board of Trustees independently of and to the exclusion of any plan or system applicable to or affecting other employees of the municipality.