Section 13-524. Other provisions relative to contributions of members

a.
  Subject  to  the  provisions  of  subdivision  b  of  this  section,   a
  contributor  shall  not  be  required  to  continue to contribute to the
  annuity savings fund after he or she  shall  have  become  eligible  for
  service retirement. All contributions made thereafter to such fund shall
  be  voluntary.  However,  this  subdivision  a  shall  not  apply  to  a
  contributor who elects to contribute at a rate not in excess of  fifteen
  per  centum  in  accordance  with  the  provisions of subdivision two of
  section 13-521 and paragraph d of subdivision one of section 13-554,  as
  amended;  nor  shall  this  subdivision  apply  to a member who became a
  contributor to the  teachers'  retirement  system  subsequent  to  April
  thirtieth, nineteen hundred sixty-three.
    b.   The  provisions  of  subdivision  a  of  this  section  shall  be
  inapplicable to  a  twenty-year  pension  plan  contributor  and  to  an
  age-fifty-five-increased-benefits pension plan contributor.
    c.  A  twenty-year  pension  plan contributor shall not be required to
  contribute to the retirement system after the  later  of  the  following
  dates:
    (1)  the  date  on  which  he  or  she  becomes eligible to retire for
  service; or
    (2) the date on which his or her accumulated deductions equal  his  or
  her minimum accumulation.