Western Hemisphere Travel Initiative

The requirement comes from the Intelligence Reform and Terrorism Prevention Act, enacted in 2004 in response to the terrorist attacks of September 11, 2001, and implemented in phases between 2007 and 2009.

[2] However, exemptions from the passport requirement existed for travel within the Americas by nationals of some North American jurisdictions.

[6] The second phase of the WHTI applied the passport requirement also for entry by land or sea from the Americas, effective June 1, 2009.

For entry by land or sea, in addition to the documents acceptable for entry by air, U.S. citizens could present a passport card, which was developed specifically for this purpose, with a lower cost and smaller size; and U.S. and Canadian citizens could present an enhanced driver's license or a trusted traveler card (FAST or SENTRI).

It also did not affect the passport exemption for holders of a U.S. permanent resident card or similar immigration document, or for travel between the United States and its territories.

[1] As a result of the WHTI, combined with previously existing requirements and subsequent changes, travelers must present one of the following documents when entering or departing the United States by air, or entering the United States by sea from outside the Americas:[7] For entry by land or sea from the Americas, travelers must present one of the documents acceptable for entry by air or one of the following:[7] Nationals of Mexico may use a Border Crossing Card, which serves as a visa when presented with a passport.