49 CFR 1103.14: Private communications with the Board are prohibited.

To the extent that the Board acts in a quasi-judicial capacity, it is improper for litigants, directly or through any counsel or representative, to communicate privately with a Board Member, administrative law judge, or other representative of the Board about a pending case, or to argue privately the merits thereof in the absence of the adversaries or without notice to them. Practitioners at all times shall scrupulously refrain from going beyond ex parte representations which are clearly proper in view of the administrative work of the Board in their communication with the Board and its staff.