27 C.F.R. § 17.112
A surety on any bond required by this part may at any time, in writing, notify the principal and the appropriate TTB officer in whose office the bond is on file that the surety desires, after a date named, to be relieved of liability under the bond. Unless the notice is withdrawn, in writing, before the date named in it, the notice shall take effect on that date. The date shall not be less than 60 days after the date on which both the notice and proof of service on the principal have been received by the appropriate TTB officer. The surety shall deliver one copy of the notice to the principal and the original to the appropriate TTB officer. The surety shall also file with the appropriate TTB officer an acknowledgment or other proof of service on the principal.
27 C.F.R. § 17.112