Requests for revision or cancellation of purchase orders on file with the Comptroller shall be submitted on a "Purchase Order Change Notice Form" bearing detailed explanation. Change orders cancelling purchase orders will not be accepted for the purpose of freeing funds. When a cancellation is made with the Comptroller, it must be made with the vendor.
N.Y. Comp. Codes R. & Regs. Tit. 2 § 7.11