The appeal referee to whom the appeal is assigned, after affording the parties reasonable opportunity for a fair hearing, shall make findings and conclusions, and on the basis thereof affirm, modify, or reverse such determination; provided, however, that whenever an appeal involves a question as to whether services were performed by claimant in employment or for an employer, or as to amount of wages reported by an employer for claimant, the tribunal referee shall give special notice of such issue and of the pendency of the appeal by mail to the employer and to the Commission, both of whom shall thenceforth be parties to the proceeding and be afforded a reasonable opportunity to adduce evidence bearing on such questions; provided, that any party who enters an appearance before the tribunal referee waives the requirement of special notice by mail.