19 CFR §146.3

1. (a)Assignment of Customs officers. Customs officers will be assigned or detailed to a zone as necessary to maintain appropriate Customs supervision of merchandise and records pertaining thereto in the zone, and to protect the revenue.
2. (b)Supervision. Customs supervision over any zone or transaction provided for in this part will be in accordance with § 101.2(c) of this chapter. The port director may direct a Customs officer to supervise any transaction or procedure at a zone. Supervision may be performed through a periodic audit of the operator's records, quantity count of goods in a zone inventory, spot check of selected transactions or procedures, or review of recordkeeping, security, or conditions of storage in a zone.