All parties, except individuals appearing in their own behalf, shall be represented by attorneys-at-law, who are duly admitted and enrolled to practice before the Court of Appeals of this State when the Commission is performing a quasi-judicial function as distinguished from a legislative, executive, or a ministerial function. A nonresident attorney may not be allowed to enter his appearance in a case before the Commission except upon motion, which will not ordinarily be granted unless some attorney with a full-time office in this State is associated with him or her in the matter.