A contract executed under this chapter must require the work to be done pursuant to the plans and specifications on file in the office of the city auditor, subject to the approval of the city auditor acting for the municipality, and must provide:
The city auditor acting for the municipality shall supervise and inspect the work during its progress. In addition to any rights which a municipality may have under its contract for establishment and operation of part or all of a business improvement after a contract has been awarded and before contract work has been completed, a municipality may, with the consent of the other party and without advertising for bids, order additional work done by that party of the same character as that which was contracted for, whether within or without the improvement district for which the original contract was made, and upon the same terms and conditions specified in the original contract except as to time of performance, and at the same prices for the additional work; provided, that the total price payable to said party for such additional work may not exceed twenty percent of the amount estimated by the city auditor for the municipality to be payable for that character of work under the original contract.
N.D.C.C. § 40-22.1-10