N.Y.C. Admin. Code § 5-204: § 5-204 Cancellation of city obligations held by the several sinking funds.

It shall be lawful for the comptroller in his or her discretion from time to time but not before maturity, to cancel any portion of the indebtedness of the city incurred on or after January first, eighteen hundred ninety-eight, which may be held by him or her in any sinking fund of the city established prior to July first, nineteen hundred eighty-one and which may by law be redeemable from such sinking fund.