53 Pa. Stat. § 881.203
Where a municipality elects to join the system established by this act, and is then maintaining a retirement or pension system or systems covering its employes in whole or in part, those employes so covered, and employes thereafter eligible to join such pension system, shall not become members of the retirement system established by this act, unless at the time the municipality elects to join the system, the members of each such existing retirement or pension system shall, by the affirmative vote of seventy-five per cent of all the members of each pension system, elect to be covered by the retirement system established by this act. At any time thereafter, within a period of three years after the municipality has elected to join the system, but not thereafter, the members of an existing retirement or pension system may, in like manner, elect to join the system established by this act. In any such case, provisions may be made for the transfer of moneys and securities in its retirement or pension fund or funds, in whole or in part, to the fund established by this act. Securities so transferred shall be only those acceptable to the board. Securities not so acceptable shall be converted into cash, and said cash transferred to the fund created by this act. In any such transfer, provision shall be made to credit the accumulated deductions of each member, at least the amount he has paid into the retirement or pension system of the municipality, which moneys shall be credited against the prior service contributions of such member, or a municipality may turn over to the retirement system created by this act any existing local pension system on a completely funded basis, as to pensioners and pension credits of members related to prior service to the date of transfer, or on a partially funded basis if the municipality pays annually into the retirement system amounts sufficient to completely liquidate the municipality's liability for prior service within a period not to exceed thirty years.
No liability, on account of retirement allowances or pensions being paid from any retirement or pension fund of the municipality, shall attach against the fund, except as provided in the agreement, making a transfer of an existing system in accordance with this section. The liability to continue payment of pensions not so transferred shall attach against the municipality, which shall annually make appropriations from its tax revenues sufficient to pay the same. In cases where workers covered by an existing retirement or pension system elect to join the system created by this act, the election to join shall be deemed to have been made at the time the municipality elected to join the system, and the liabilities of the municipality shall be fixed accordingly.
If a municipality elects to join the system under the provisions of this Article II, then each officer other than elected officers, and each municipal employe employed on a full-time basis, except one who is not eligible for Federal Social Security coverage and except one who is covered by an existing retirement or pension system and is exempted as outlined above, shall be required to become a member of the system. Each municipality shall determine whether membership in said system for elected officials and employes hired on a temporary, seasonal or part-time basis shall be compulsory, optional or prohibited. Where membership may be optional with an elected officer or an employe hired on a temporary, seasonal or part-time basis, an election to join the system must be made within one year after the municipality elected to join the system or within one year after the officer or temporary, seasonal or part-time employe first entered the service of the municipality. Officers and employes paid only on a fee basis shall not be eligible to join the system.
When a municipality has established a policy of placing new employes on a probationary status it may elect to refrain from enrolling such employes into the system for a period of up to one year from the date the probationary employe first entered the service of the municipality. In such cases service credits shall not be earned by the employe for probationary time served prior to enrollment.
Notwithstanding any other provision herein, the board may, in its discretion, entertain a request from a municipality to join the system established by this act for those employes who are excluded from local pension plan coverage by virtue of the collective bargaining process or otherwise. The request to join the system must be accompanied by an affirmative vote of no less than three-fourths of those employes not covered by the local pension plan. The benefits to be established may be in accordance with the provisions of this article or any other relevant pension law covering that class of municipality. The other requirements of this section for joining this system shall be observed.
53 P.S. § 881.203