UPS and FedEx will not accept cremated remains for shipment. Should the question come up, the requirements related to shipping cremated remains by the US Postal Service are as follows:
US Postal Service
Publication 52 - Hazardous, Restricted, and Perishable Mail
4 Restricted Matter
45 Liquids, Powders, and Odor-Producing Materials
a. Liquids and powders that are nonhazardous (i.e., not regulated as hazardous materials) are mailable provided they are properly packaged as specified in 453 and DMM 601.12.9.1 and DMM 601.12.9.2.
b. Any matter that is a source of an obnoxious odor is nonmailable as stated in DMM 601.12.8.
Liquids and powders that are corrosive, explosive, flammable, toxic, or otherwise hazardous are subject to the mailing conditions for hazardous materials in chapter 3 and DMM 601.10, as applicable.
452.2 Cremated Remains
The following applies when mailing human ashes (cremated remains):
a. Domestic. Permitted only when sent via Priority Mail Express service or when using Registered Mail service (see DMM 503.2). The identity of the contents should be marked on the address side, and the item must be packaged as required in 453b.
b. International. Permitted only when sent via Priority Mail Express International™ service (when available to the destination country), or First-Class Package International Service using Registered Mail service (when available to the destination country). The identity of the contents must be indicated on the applicable customs declaration form, and the item must be packaged as required in 453b.
SOURCE (Accessed 11 January 2014)