The board of trustees may allow its employees to become members of a retirement or pension plan of the county where the hospital is located or it may establish its own retirement or pension plan for its employees. Before a plan established by the board of trustees shall become effective or operative, it shall be approved by the county pension plan committee created by section 12a of Act No. 156 of the Public Acts of 1851, as amended, being section 46.12a of the Compiled Laws of 1948.