The Secretary, after due notice and opportunity for hearing, may suspend or disbar from practice before the Bureau any attorney, certified public accountant, or enrolled practitioner shown to be incompetent, disreputable or who refuses to comply with the rules and regulations in this part or who shall, with intent to defraud, in any manner willfully and knowingly deceive, mislead, or threaten any client or prospective client, by word, circular, letter, or by advertisement.