37 C.F.R. §2.17(f) Non-lawyers.
A non-lawyer may not act as a representative except in the limited circumstances set forth in §11.14(b) of this chapter. Before any non-lawyer who meets the requirements of §11.14(b) of this chapter may take action of any kind with respect to an application, registration or proceeding, a written authorization must be filed, signed by the applicant, registrant, or party to the proceeding, or by someone with legal authority to bind the applicant, registrant, or party (e.g., a corporate officer or general partner of a partnership).
37 C.F.R. §11.14(b) Non-lawyers.
Individuals who are not attorneys are not recognized to practice before the Office in trademark and other non-patent matters, except that individuals not attorneys who were recognized to practice before the Office in trademark matters under this chapter prior to January 1, 1957, will be recognized as agents to continue practice before the Office in trademark matters. Except as provided in the preceding sentence, registration as a patent agent does not itself entitle an individual to practice before the Office in trademark matters.
Non-attorneys are not permitted to practice except under the limited circumstances specified in 37 C.F.R. §11.14(b), set forth above. 5 U.S.C. §§500(b), (d); 37 C.F.R. §§2.17(f), 11.14(e).