19 CFR § 142.3a - Entry numbers.
(a) Placement on CBP forms. The importer or broker shall place an 11 character entry number on the entry and corresponding entry summary documentation. For documentation prepared on data processing equipment, the number shall be printed directly on the form. For manually prepared documentation, the number shall be pre-printed in a machine readable format specified by CBP. The same number shall not be used for more than one entry transaction.
(b) Format. The following format, including hyphens, must be used when showing the entry number:
(1) Assignment of entry filer code. CBP will assign a unique 3 character (alphabetic, numeric, or alpha numeric) entry filer code to all licensed brokers filing CBP entries. CBP will assign an entry filer code to certain importers filing CBP entries based on importer entry volume, frequency of entry filing, and other considerations. The broker or importer shall use this assigned code as the beginning three characters of the number for all CBP entries, regardless of where the entries are filed.
(2) Entry filer assigned number. For each entry, the broker or importer shall assign a unique 7 digit number. This number shall not be assigned to more than one transaction.
(3) Check digit. The broker or importer is responsible for ensuring that the check digit is computed by data processing equipment.
(c) Pulication of entry filer codes. CBP shall make available electronically a listing of filer codes and the importers, consignees, and customs brokers assigned those filer codes. The listing will be updated periodically.
(d) Misuse of the entry filer code. The Assistant Commissioner, Office of International Trade, or his designee may refuse to allow use of an assigned entry filer code if it is misused by the importer or broker.
(e) Alternative procedure. If an importer does not have an assigned entry filer code, or if the Assistant Commissioner, Office of International Trade, or his designee, in accordance with paragraph (d) of this section ref uses to allow use of an assigned entry filer code, the importer or broker shall obtain forms with a CBP assigned pre-printed machine readable entry number with a computed check digit. These forms will be available for sale by CBP and must be obtained and used before the merchandise may be released from CBP custody.