The claimant or any other party entitled to a notice of a determination as provided in the North Dakota unemployment compensation law may file an appeal from such determination with the appeal tribunal within twelve days after the date of mailing of the notice to the person‘s    last-known address or, if such notice is not mailed, within twelve days after the service of such notice. Unless the appeal is withdrawn with the permission of the appeal tribunal or is removed to the bureau, the appeal tribunal after affording the parties reasonable opportunity for a fair hearing shall make findings and conclusions and on the basis thereof shall affirm, modify, or reverse such determination. Whenever an appeal involves a question as to whether services were performed by the claimant in employment or for an employer, the tribunal shall give special notice of such issue and of the pendency of the appeal to the employing unit and to the bureau, both of whom thenceforth shall be parties to the proceeding and must be afforded a reasonable opportunity to adduce evidence bearing on such question.