N.D. Cent. Code § 52-04-10
The bureau shall promptly make a determination and notify each employer of the employer's rate of contributions as determined for each ensuing year by the end of the first full week of December, but not later than December tenth, of the preceding year. The rate of contributions must be computed pursuant to the provisions of this chapter. The determination becomes conclusive and binding upon the employer unless, within fifteen calendar days after the mailing of the notice thereof to the employer's last-known address, or in the absence of the mailing, within fifteen calendar days after the delivery of such notice, the employer files a written appeal of the determination. However, no employer shall have standing, in any proceeding involving the employer's rate of contributions or contribution liability, to contest the chargeability to the employer's account of any benefits paid in accordance with a determination, redetermination, or decision pursuant to the provisions of chapter 52-06, except upon the ground that the services on the basis of which such benefits were found to be chargeable did not constitute services performed in employment for the employer and only in the event that the employer was not a party to such determination, redetermination, or decision or to any other administrative proceeding in which the character of these services was determined. For purposes of this section, an employer was not a party to any such proceeding if notice of the determination, redetermination, or decision and the employer's right to appeal the determination, redetermination, or decision was not mailed or personally delivered to the employer.
N.D.C.C. § 52-04-10