19 CFR § 151.2 - Quantities to be examined.
(a)
(1) Minimum quantities. Not less than one package of every 10 packages of merchandise shall be examined, unless a special regulation permits a lesser number of packages to be examined. Port directors are specially authorized to examine less than one package of every 10 packages, but not less than one package of every invoice, in the case of any merchandise which is:
(i) Imported in packages the contents and values of which are uniform, or
(ii) Imported in packages the contents of which are identical as to character although differing as to quantity and value per package.
(2) Exceptions to minimum quantities. At ports of entry specifically designated by the Commissioner of Customs, the port director is authorized to release, without examination, merchandise of a character which the port director has determined need not be examined in every instance to ensure the protection of the revenue and compliance with the Customs laws and any other laws enforced by the Customs Service.