"Considerable controversy continues to surround U.S. air passenger prescreening and terrorist watchlist checks. In the past, such controversy centered around diverted international flights and misidentified passengers. While screening agencies have taken some steps to ameliorate those problems, other related issues have arisen, underscoring that screening passengers for more intensive searches of their person or baggage, or to prevent them from boarding an aircraft in the event of a terrorist watchlist hit, is likely to be a difficult proposition for the federal agencies tasked with aviation and border security, principally the Department of Homeland Security (DHS), Transportation Security Administration (TSA), and Customs and Border Protection (CBP). Recent developments underscore the difficulties encountered by frontline-screening agencies. […] In addition, CBP has sought greater amounts of PNR [passenger name record] data preflight from all air carriers and to retain that data for a greater length of time. U.S. authorities maintain that these measures are necessary to provide greater aviation and border security. In July 2006, however, the European Court of Justice ruled that the existing agreement between the European Commission and CBP to exchange PNRs was illegal. The court ordered the cessation of this data exchange on September 30, 2006. While a new agreement was reached in October 2006, this impasse could have significantly affected travel from European Union countries to the United States. Moreover, the agreement is temporary and is set to expire on July 31, 2007."
CRS Report for Congress, RL33645