No attorney, certified public accountant or enrolled practitioner shall, in practice before the Bureau, knowingly and directly or indirectly:
(a) Employ or accept assistance from any person who is under disbarment or suspension from practice before any agency of the Treasury Department;
(b) Accept employment as associate, correspondent, or subagent from, or share fees with, any such person;
(c) Accept assistance in a specific matter from any person who participated personally and substantially in the matter as an employee of the Treasury Department. [44 FR 47059, Aug. 10, 1979]