Tangible personal property imported from outside the United States and held in a zone for the purpose of storage, sale, exhibition, repackaging, assembly, distribution, sorting, grading, cleaning, mixing, display, manufacturing, or processing, and tangible personal property produced in the United States and held in a zone for exportation, either in its original form or as altered by any of the above processes, shall be exempt from State and local ad valorem taxation.
19 U.S. Code § 81o. Residents of zone
(a) Persons allowed to reside in zone
(b) Rules and regulations for employees entering and leaving zone
(c) Exclusion from zone of goods or process of treatment
(d) Retail trade within zone
(e) Exemption from State and local ad valorem taxation of tangible personal property