53 Pa. Stat. § 881.405
Each member of the system shall be required to contribute to the fund such per cent of his actual salary or compensation, including fees where paid in part on a fee basis, as specified in the contract, which contributions shall be paid into the fund by the municipality through payroll deductions in such manner and at such time as the board may by rule and regulation determine.
If such provision is contained in the contract between the municipality and the board, each member may increase his member's annuity by electing to make such additional voluntary contributions as prescribed therein.
When a member is employed by more than one municipality, he shall be required to make contributions on account of his salary paid by each municipality. In such cases the board shall provide for the consolidation of credits of the contributor, and upon his retirement, for a consolidated retirement allowance.
When a contributor leaves the employ of a municipality which has joined the system, and enters into the employ of another municipality which has also joined the system, his service credits shall remain unimpaired, but in such cases any unpaid municipal liability for prior service shall be prorated by the board between the municipalities on an equitable basis.
53 P.S. § 881.405