27 CFR 24.116: Powers of attorney.

The proprietor shall file with the appropriate TTB officer a power of attorney for each person authorized to sign or to act on behalf of the proprietor as an attorney-in-fact. A power of attorney is not required for any person whose authority has been furnished in the application. If not limited in duration, the power of attorney will continue in effect until written notice of revocation is received by the appropriate TTB officer or operations are terminated.