N.Y.C. Admin. Code § 6-110: § 6-110 Additional work.

Any contract for work or supplies may contain a provision to the effect that the head of the agency making the contract may order additional work to be done or supplies furnished for the purpose of completing such contract, at an expense not exceeding five per centum of the amount thereof; provided, however, that the board of estimate may by resolution adopt regulations providing that any contract for work or supplies may contain a provision to the effect that the head of the agency making the contract may order additional work to be done or supplies furnished for the purpose of completing such contract, at an expense not exceeding ten per centum of the amount thereof.