The new rules, which also apply to the Caribbean, are aimed at improving security, but CNN said there are concerns they will slow down business travel and could also trip up U.S. vacationers used to driving across the border with just their driver's license.
"I guarantee you there's someone in Kansas or someone in Ottawa who's never even heard what WHTI (Western Hemisphere Travel Initiative ID card) is, who is used to going on their summer vacation with their driver's license," said Roger Dow president of the U.S. Travel Association.
The Department of Homeland Security said it would begin enforcement of the rules in a "soft" fashion and estimated that up to 90 percent of Americans who make routine border crossings already have the required documentation.
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