14 CFR § 300.6 - Practitioners' standards of conduct.
Every person representing a client in matters before DOT in all contacts with DOT employees, should:
(a) Strictly observe the standards of professional conduct;
(b) Refrain from statements or other actions designed to mislead DOT or to cause unwarranted delay;
(c) Avoid offensive or intemperate behavior;
(d) Advise all clients to avoid improprieties and to obey the law as the attorney believes it to be; and
(e) Terminate the professional relationship with any client who persists in improprieties in proceedings before DOT.