The implementation of the new requirement was named the Western Hemisphere Travel Initiative (WHTI) and was done in phases. In the first phase, effective January 23, 2007, nationals of the United States, Canada, Bermuda and Mexico became required to present a passport to enter the United States by air from the Americas. The regulations retained exceptions for U.S. and Canadian citizens with a NEXUS card, and for members of the U.S. military and U.S. Merchant Marine.Documents Required for Travelers Departing From or Arriving in the United States at Air Ports-of-Entry From Within the Western Hemisphere, Federal Register, November 24, 2006.
