I looked this up the other day and came across the following on TSA.gov: "Even prior to the passage of ATSA and the Federalization of the screening work force,

I looked this up the other day and came across the following on TSA.gov: "Even prior to the passage of ATSA and the Federalization of the screening work force, Federal courts upheld warrantless searches of carry-on luggage at airports. Courts characterize the routine administrative search conducted at a security checkpoint as a warrantless search, subject to the reasonableness requirements of the Fourth Amendment. Such a warrantless search, also known as an administrative search, is valid under the Fourth Amendment if it is "no more intrusive or intensive than necessary, in light of current technology, to detect weapons or explosives, " confined in good faith to that purpose," and passengers may avoid the search by electing not to fly. [See United States v. Davis, 482 F.2d 893, 908 (9th Cir. 1973)]. While the searches at the airport will be conducted by private screening companies, such searches will continue to be subject to the Fourth Amendment requirements of reasonableness because they are conducted at the instigation of the federal Government and under the authority of federal statutes and regulations governing air passenger screening." --http://www.tsa.gov/what_we_do/optout/spp_faqs.shtm http://www.tsa.gov/what_we_do/optout/spp_faqs.shtm (search for "amendment")