39 CFR § 320.7 - Suspension for advertisements accompanying parcels or periodicals.
(a) The operation of 39 U.S.C. 601(a) (1) through (6) and § 310.2(b) (1) through (6) of this chapter is suspended on all post routes for advertisements enclosed with merchandise in parcels or accompanying periodicals under the following circumstances:
(1) The advertisements must not be marked with the names or addresses of the intended recipients.
(2) The advertisements must be incidental to the shipment of the merchandise or the periodical.
(i) An advertisement is incidental to the shipment of the accompanying merchandise or the periodical when the merchandise or the periodical has been ordered by or would otherwise be sent to the recipient even without the accompanying advertisement.
(ii) Notwithstanding § 320.7(a)(2)(i), an advertisement is not incidental to the merchandise when the pertinent circumstances, such as the nominal value of the merchandise, its shipment on an unsolicited basis, or its status as a sample, reasonably indicate that the shipper's primary purpose is the conveyance of the advertisement itself and that the merchandise is merely an adjunct to the advertisement.
(b) An item is an advertisement if its primary purpose is to cause or induce the purchase of goods or services from the shipper or others.