Past indiscretions are coming back to haunt thousands of American travelers as Canadian border guards use improved technology to screen for criminal records.

The sharing of computerized information and increased vigilance since Sept. 11, 2001, have led more than 18,000 U.S. citizens with criminal records to be turned away since 2003. The records often date back to the distant past for offenses like marijuana possession, assault and impaired driving.

The Canada Border Services Agency says the number of so-called "turnbacks" from the border has declined gradually in recent years. About 3,430 people were turned away among 28.9 million visitors in 2006, compared with 5,876 who were denied entry among 35.5 million visitors in 2003.

But immigration lawyers operating on both sides of the border maintain they've seen a recent spike in complaints from rejected Americans.

"There is a net that has been cast that is catching all these minnows," said David Cohen, a Montreal-based immigration lawyer.

Cohen and other lawyers say they receive frequent inquiries from Americans with minor records who wonder what they have to do to get back into Canada. Many had traveled to Canada for years without a problem.

Cohen has received calls from professional athletes, airline pilots and truckers who were suddenly turned away. Cohen says 90 percent of his calls are related to driving under the influence of alcohol.

Chris Williams of the CBSA pointed to the declining "turnback" statistics and said there is no crackdown.

"The laws haven't changed, each traveler is processed on a case-by-case basis, based on information they provide and information available to each officer," Williams said.

Detroit immigration lawyer Enrico Caruso tells of an American lawyer with a practice in Toronto who was turned back at the border because he was busted in his youth for scalping Detroit Red Wings tickets.

"The laws have not changed but there have been major changes in technology," said Caruso, who practices in Canada and the United States. "Their databases are syncing up really well, so they see a lot more information on their computers."

But Caruso says visitors traveling in both directions face more questions crossing the border.