1. All persons who enter or reenter the service of the such cities as police officers for compensation after the date this police retirement system becomes effective shall become members thereof as a condition of their employment.

2. Members of the police retirement system shall receive no retirement or pension allowance from any other retirement or pension system supported wholly or in part by such cities or the state of Missouri, nor shall they be required to make contributions under any other retirement or pension system of such cities or the state.

3. Nothing in sections 86.900 to 86.1280 shall be construed to prevent the inauguration of the federal Social Security laws for police officers, nor to prevent the contribution to such Social Security administration or fund established by the federal government, nor by it the pensioning of such police officers. In the event that federal Social Security benefits are made available to police officers covered by sections 86.900 to 86.1280, then any benefits payable to any member or the dependents of such member under sections 86.900 to 86.1280 shall be in addition to the amount of such Social Security benefits, and any contributions required by a member under this section shall be in addition to the amount of such member’s contribution under such Social Security system.