49 CFR §1103.25

1. (a)A practitioner shall always treat adverse witnesses and other litigants with fairness and due consideration. He should never minister to the prejudice of a client in a trial or conduct in a cause. The client has no right to demand that the practitioner representing him abuse the opposing party or indulge in offensive personal attacks.
2. (b)A practitioner shall not attempt to obstruct Board investigations or corruptly to influence witnesses and potential witnesses during an investigation.
3. (c)In conducting a case it is improper for a practitioner to allude to the personal history or the personal peculiarities or idiosyncracies of practitioners on the other side, or otherwise engage in personal abuse of other practitioners.