A budding cross-border data exchange with the United States is quietly helping Canada crack down on immigration violators.

The federal government has flagged more than 1,000 possible cases of people overstaying their visas or committing other immigration infractions based on information provided by the United States, newly obtained memos show.

Under a 2011 continental security pact, Canada and the United States agreed to set up co-ordinated systems to track the entry and exit information of travellers.

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The effort involves exchanging entry information collected from people at the land border — so that data on entry to one country serves as a record of exit from the other.

Canada says the information will be helpful in everything from tracking known fugitives to responding more effectively to missing-child alerts.

The federal NDP and privacy advocates are watching closely, however, out of concern the data could be used to build invasive personal profiles with little accountability.

The data includes the traveller's name, nationality, date of birth and gender, the country that issued their travel document and the time, date and location of their crossing.

The first two phases of the program were limited to foreign nationals and permanent residents of Canada and the U.S., but not citizens of either country.

Canada's border agency has begun sharing information with U.S. Homeland Security about the thousands of American citizens who cross into Canada each day. Legislation being debated in Parliament would allow Ottawa to collect similar information about Canadians entering the U.S.

But the newly disclosed memos say the preliminary phases are already helping Canada zero in on people who may be running afoul of immigration laws.

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Between June 2013 and October 2015, Canada received nine million exit records from the U.S., resulting in over 1,000 cases being referred to immigration officials. Such data is helpful in identifying visitors who stay in Canada longer than their visa allows.

It can also establish that someone has left Canada, leading to cancellation of 26 immigration warrants and 69 removal orders during the period.

The Canadian Press used the Access to Information Act to obtain the figures from the Canada Border Services Agency, a process that took 18 months. A complaint to the federal information commissioner helped dislodge the pages.

The number of immigration enforcement actions is almost certainly larger than 1,000, given that the figures do not cover the most recent two years. However, the border agency was unable to provide updated numbers.

Once the legislation is passed, information-sharing on all travellers crossing the land border will take place.

Canada also plans to begin collecting information on people leaving by plane — something the United States already does — by requiring airlines to submit passenger manifest data for outbound international flights. This information would not be shared with the U.S.

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The border agency says the fuller data streams will improve monitoring of visa compliance.

Canada also intends to use the information to track high-risk travellers such as fugitives, suspected terrorists, registered sex offenders, smugglers and exporters of illegal goods.

In addition, the data will help verify whether people have complied with residency requirements and determine their entitlement to social benefits, which may require a presence in Canada.

The NDP is skeptical of the need to expand information-sharing with the U.S. and wary of the implications for Canadians in the era of "false positives" that can land people in trouble or deny them entitlements, said Matthew Dube, the party's public safety critic.

"Mistakes can be very costly in those circumstances for people."

The program's scope underscores the need for strong, clear rules concerning use of the data and steps to ensure its accuracy, said Tim McSorley, national co-ordinator of the Ottawa-based International Civil Liberties Monitoring Group.

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McSorley wonders whether the Canadian Security Intelligence Service would be permitted to sift through the files to try to discern travel patterns, given the spy service's interest in datasets. "And then what are the protections that would be afforded there?"

He would also like assurances that Canadians will be able to request and see copies of the travel data in order to correct any discrepancies.