New regulations took effect Tuesday, requiring all travelers from the United States, Canada, Mexico and Bermuda to present passports in order to enter the United States when arriving by air from any part of the Western Hemisphere.
Before now, other forms of identification, such as drivers licenses, were accepted.
The rule change was suggested by the bipartisan commission investigating the September 11, 2001 terrorist attacks, and passed into law by the U.S. Congress.
U.S. officials say next year, Americans traveling in the Western Hemisphere by land or sea could be required to present a valid American passport to get back into the United States.
Some information for this report was provided by AP.