37 C.F.R. § 41.108 – Lead counsel.

(a) A party may be represented by counsel. The Board may require a party to appoint a lead counsel. If counsel is not of record in a party's involved application or patent, then a power of attorney for that counsel for the party's involved application or patent must be filed with the notice required in paragraph (b) of this section.
(b) Within 14 days of the initiation of each contested case, each party must file a separate notice identifying its counsel, if any, and providing contact information for each counsel identified or, if the party has no counsel, then for the party. Contact information must, at a minimum, include:
1. (1) A mailing address;
2. (2) An address for courier delivery when the mailing address is not available for such delivery (for example, when the mailing address is a Post Office box);
3. (3) A telephone number;
4. (4) A facsimile number; and
5. (5) An electronic mail address.
(c) A party must promptly notify the Board of any change in the contact information required in paragraph (b) of this section.