27 C.F.R. § 19.171 – Surety notice of relief from bond liability.

(a) Notice to principal. A surety on a bond may, at any time, notify the principal in writing that the surety desires to be relieved of liability under the bond.
(b) Notice to TTB. A surety on a bond may, at any time, notify the appropriate TTB officer in writing that the surety desires to be relieved of liability under the bond. The notice must specify the date after which the surety desires to be relieved of liability. In the case of a withdrawal bond, the date specified in the notice must be at least ten days after the notice is received by the appropriate TTB officer. In the case of an operations bond or unit bond, the date specified in the notice must be at least 90 days after the notice is received by the appropriate TTB officer. When a surety files a termination notice with TTB, the surety must include either an acknowledgement from the principal that the principal is aware that the surety is terminating the bond or proof that the surety has served the principal with notice of its intent to terminate the bond.
(c) Effect of notice. The bond coverage will end as of close of business on the date specified in the notice, provided the surety timely filed a proper and complete termination notice, and the surety does not withdraw its termination notice in writing prior to the termination date. The surety will be released from future liability under the bond to the extent set forth in § 19.172.
(26 U.S.C. 5173, 5175, 5176)