JAY, Vermont (CNN) -- Beginning Thursday, U.S. and Canadian citizens who want to enter the United States from Canada must provide border agents with two documents: proof of citizenship such as a birth certificate and a government-issued photo identification such as a driver's license.
In the past, documents weren't required to cross the border from Canada into the United States.
The rules apply to people who are 19 and older and who do not have passports.
Until this week, U.S. and Canadian citizens have been able to enter the U.S. without any proof of citizenship. Saying they were Canadian or a U.S. citizen was sufficient.
U.S. Customs and Border Protection personnel could ask additional questions if they doubted those claims, but documents were not required.
But the new rules, which are meant to strengthen security in the United States, are causing anxiety for Americans who depend on tourism for a living.
They said they are worried that new travel security rules will keep away Canadian visitors, such as those who regularly flock to ski resorts across the border.
On Thursday, people were whizzing through at customs as border protection agents provided some leeway until Canadians and U.S. travelers get used to the new rules. Watch Canadian tourists talk about the new rules »
But people in the tourist industry remember last summer, when minor changes in document procedures at the border created hourslong backups and delays.
About 50 percent of the skiers and snowboarders who visit Vermont's Jay Peak come from north of the border. The resort makes sure Canadians feel wanted. The sign at the entrance says "Bienvenue," French for welcome. The Canadian and U.S. flags fly alongside each other over the lodge. The snack bar and ski shop accept Canadian currency.
Bill Stenger, Jay Peak's president and chief operating officer, is among those worried that the new rules requiring Canadians to show identification documents when they enter the United States will create significant backups again.
"If we lose 15, or 18, or 20 percent because of the perception of there being a problem at the border, that will hurt us. That will hurt us very significantly," Stenger said.
It is a stopgap security measure. Congress has pushed back implementation of the Western Hemisphere Travel Initiative, which will require that travelers carry passports or other approved travel documents, until at least summer 2009.
Homeland Security Secretary Michael Chertoff said in an interview that he thought the previous requirement of only an oral statement would be news to many U.S. citizens.
"I think this would frankly shock a lot of people. It certainly surprised me when I learned about it," Chertoff said.
Chertoff said the new document requirements will help secure the border at a time when the public is demanding tighter measures.
"It strikes me as a little anomalous to say we're going to build a fence between the ports of entry, but you can just walk right through the port of entry by saying, 'Hi, I'm an American citizen,' without being checked."
In a January 17 letter to Sen. Charles Schumer of New York, Chertoff wrote that during the last three months of 2007, there were more than 1,500 false oral declarations, including one person who had an outstanding arrest warrant for homicide in California. He called that person's detention a success but said, "We do not know how many false oral declarations we miss."
The new requirements have brought cries of protest from the travel industry, northern border states, their chambers of commerce and representatives in Congress.
"It's a terrible idea. It's a job killer, plain and simple," Rep. Peter Welch said. Welch, a Vermont Democrat, accused Chertoff of "putting the bureaucracy ahead of the needs of the people."
Tens of thousands of Americans and Canadians cross the border every day to jobs and families on the other side. Some communities, such as Derby Line, Vermont, even straddle the border.
Despite publicity about the new document rules, many people living near the border may not have gotten the message.
"I think there is a degree of confusion," said Chris Biber of Ottawa. "It's not just that they don't have documents; people don't know which documents are required."
Biber said his family has passports and will return to ski at Jay Peak, but he predicts other Canadians will choose not to travel to the U.S.
U.S. Customs and Border Protection has indicated it will not enforce the new rules strictly at first, but such assurances haven't allayed concerns about possible backups and delays at border crossings.
Stenger said he's expecting 500 Canadians to arrive at his ski slopes Friday. He has worked to publicize the new border requirements on his ski area's Web site, in advertisements and during the booking process.
His message is: "Have your passports. Bring your IDs. Have them ready at the border. Make it as efficient as possible. That way, hopefully, we can minimize the impact."
Stenger said the real test will come in about three weeks, when Canadian students get their winter break and head for U.S. ski slopes. By then, he said, the U.S. border agency will have tightened up enforcement of the new rules.
Stenger said he's worried about the impact on his 500 employees and tourist-reliant community.
The Canadian government estimates that 7 million jobs in the United States are directly or indirectly tied to U.S.-Canadian trade.
"Every day $1.5 billion worth of trade goes across the Canadian border. Forty million Canadians visit the U.S. every year, and 16 million stay overnight," said Roger Dow, president and CEO of the Travel Industry Association. "It's really going to have an effect."
A coalition of U.S. senators from 19 border states wrote to Chertoff this week asking him to delay implementation of the new requirements, but the secretary said it was time to end the "honor system" for crossing the border.
"I still have ringing in my ears the words of the 9/11 commission, which talks about the importance of dealing with this," Chertoff told CNN. "I frankly thought the heat I would get is, 'Why did it take so long?' and why were we still not at the end state."
Leo and Grace Mairinger of Hamilton, Ontario, said they think Chertoff is right. The couple is spending several days skiing at Jay Peak.
Leo Mairinger said that "it's only reasonable" to ask for documentation at an international border crossing. His wife agrees. "They don't know who is coming in their country. Of course, they're going to want to have proper papers," she said.
But critics said asking for birth certificates is not going to improve security. There are thousands of different kinds, and they can be counterfeited or stolen, they point out.
"We are not going to improve security on the northern border by doing this," Stenger said.
He said he also fears it will damage the cordial relationship between Canada and the United States. "You don't get a second chance at this," he said. "If they screw it up, the memories will be long-lasting." E-mail to a friend