71 Fed. Reg. 68412 (November 24, 2006)
The Department of State and the Bureau of Customs and Border Protection published a final rule to implement Phase One of the Western Hemisphere Travel Initiative (WHTI). The rule, effective January 23, 2007, requires valid passports of all U.S. citizens as well as all nonimmigrant aliens with citizenship in Canada, Bermuda, and Mexico, departing from or entering the United States from within the Western Hemisphere at air ports-of-entry. Prior to this, these individuals were exempt from the passport requirement. This rule does not change visa rules, only travel document requirements. A separate, future rulemaking will address land and sea travelers.