Section 178. Additional limitations on eligible investments

Notwithstanding any other provision of law, including the provisions  of
  the administrative code of the city of New York, the trustee or trustees
  of  a fund shall not have the power to invest in any insured mortgage or
  conventional mortgage of an unpaid  principal  amount  at  the  time  of
  investment  of  less  than two hundred fifty thousand dollars; provided,
  however,  that  this  limitation  shall  be  inapplicable  as  to  those
  mortgages  pledged,  assigned  or  transferred to the fund as collateral
  security for the unpaid balance of the bonds and  notes  purchased  from
  any  bank,  trust  company, savings bank or savings and loan association
  authorized by subdivision four of section one hundred  seventy-seven  of
  this  chapter;  and  provided  further  that,  with  respect to any fund
  administered for employees of the city  of  New  York,  the  trustee  or
  trustees  of  such  a  fund shall be authorized to invest in any insured
  mortgage or conventional mortgage of an unpaid principal amount  at  the
  time of investment of not less than one hundred thousand dollars.