On all planning commissions appointed pursuant to the Pennsylvania Municipalities Planning Code, Act 247, as amended, a certain number of the members, designated as "citizen members," shall not be officers or employees of the municipality. On a commission of three members, at least two shall be citizen members. On a commission of four or five members, at least three shall be citizen members. On a commission of either six or seven members, at least five shall be citizen members, and on commissions of either eight or nine members, at least six shall be citizen members.