
"UPS guarantees on-schedule delivery of packages shipped via UPS Worldwide Express Plus, UPS Worldwide Express NA1, UPS Worldwide Express, UPS Worldwide Expedited, UPS 3 Day Select From Canada and UPS Standard, where such services are available and provided that the customs clearance is performed by the UPS Supply Chain Solutions brokerage offices designated by UPS for clearing these products and there is not a delay caused by certain events beyond our control, such as a government agency hold.
Customs clearance for the products listed above are provided by the UPS Supply Chain Solutions brokerage offices (formerly UPS Customhouse Brokerage offices) designated for handling small package customs clearance. Other UPS Supply Chain Solutions customs brokerage offices charge fees for clearance of small packages and freight."
The above excerpt is from page 149 of the following PDF file provided on UPS' Web site:
http://www.ups.com/media/en/service_guide_us_daily.pdf