Period of retention.
All records and files, all documents or copies of documents supporting these records and files, and all file copies of reports, submitted as required by this part, must be retained by the person required to have them, for a period of not less than three years and, during the retention period, must be available, during business hours, for inspection and copying by the appropriate TTB officers. In addition, the appropriate TTB officer may require retention of the documents and other records for an additional period of not more than three years if it is determined that such additional retention is necessary.
26 U.S.C. 5123