Section 13-308. Credit for certain prior city service

Any person who was a
  member of the New York city  employees'  retirement  system,  and  whose
  membership  therein was terminated by his or her attaining membership in
  the fire department pension fund, subchapter one, and who had  withdrawn
  his  or  her  contributions  to  the New York city employees' retirement
  system, shall receive credit in the said fire  department  pension  fund
  for  prior  creditable  city  service  by  paying  into  the  said  fire
  department  pension  fund  the  amount  of  the  employee  contributions
  required  to have been paid into the New York city employees' retirement
  system for such prior creditable city service, within  two  years  after
  this  act  shall  take  effect, provided, however, that no member of the
  said fire department pension fund shall be eligible for  retirement  for
  service  until he or she has served in the fire department for a minimim
  period of twenty or twenty-five years, according to the  minimum  period
  of  retirement  elected by such member prior to the certification of his
  or her rate of contribution.