The federal government says it is looking into whether the enforcement of U.S. President Donald Trump's executive order banning entry of certain nationalities to the United States violates Canadian laws.

Trump signed an executive order more than a week ago, restricting entry to the United States for travellers from seven predominantly Muslim countries.

Canada is one of only six countries that has U.S. border agents working on its national territory under a long-standing agreement that allows travellers to pre-clear customs at major Canadian airports and other departure points. The agreement is set to expand under a bill passed by the U.S. Congress in December.

Because those operations by U.S. customs agents are carried out on Canadian soil, they are subject to Canadian laws.

Andrew Gowing, a spokesman for Public Safety Canada, told CBC News, "The government is still in the process of determining what, if any, impact the recent U.S. executive order has on current pre-clearance activities or on the Agreement on Land, Rail, Marine and Air Transport Preclearance" between the countries.

"Any U.S. pre-clearance activities in Canada have to be carried out in a manner consistent with Canadian law, including the Canadian Charter of Rights and Freedoms, the Canadian Bill of Rights and the Canadian Human Rights Act."

Convenience for Canadians

Pre-clearance allows Canadian travellers to clear both U.S. Customs and immigration controls at their point of departure, and has existed since 1952 in Canada.

As a result of pre-clearance, Canadians can land directly at smaller U.S. domestic airports that lack customs and immigration facilities.

U.S. Customs Calgary airport

Passengers wait to check in and go through U.S. Customs at Calgary International Airport in Calgary in 2009. The Canadian government is considering how the recent U.S. travel ban affects a long-standing pre-clearance agreement between the two countries. (Todd Korol/Reuters)

The system currently operates at eight Canadian airports: Halifax, Montreal, Ottawa, Toronto, Winnipeg, Calgary, Edmonton, and Vancouver. It also operates at the Port of Vancouver, and at the city's Pacific Central train station, and on some B.C.-Washington ferries.

Under an agreement signed last March, U.S. border agents are scheduled to begin working this year in three additional ports of departure: Toronto Island airport, Quebec City's airport, and Montreal's Central Station.

The expansion and the existing arrangement would be in danger if the new executive order were found to be inconsistent with Canadian laws or the Charter.

Ireland, Netherlands have concerns

The only other countries that have pre-clearance agreements with the U.S. are Ireland, Aruba, the Bahamas, Bermuda and the United Arab Emirates.

Ireland, the only country in Europe that has U.S. border agents on its soil, has ordered a review to see whether the Trump order violates the country's anti-discrimination laws.

The review came after a man living legally in Ireland was refused pre-clearance at Dublin airport. The Irish government has not disclosed the identity of the man, but has said that in his view he should have been allowed to travel.

Irish Prime Minister Enda Kenny has said he would like to keep pre-clearance facilities, which have made travel between the U.S. and Ireland much easier.

Kevin Toland, chief executive of the Dublin Airport Authority, said the pre-clearance facility was a "critical point of competitive advantage for Ireland … critically important for this country, critically important for the government, critically important for our airport, and critically important for the U.S."

But some in the government say that should not trump Irish law, including Minister for Children Katherine Zappone, whose tweets about the issue led to the review.

Zappone tweet

Irish cabinet minister Katherine Zappone was the first to question the pre-clearance agreement in her government.

The Netherlands has also been in talks with the U.S. since December about extending pre-clearance to its Schiphol international airport, but on Tuesday it abruptly ended them.

Foreign Minister Bert Koenders said the Trump visa ban affected some of his friends who were dual Dutch-Iranian citizens, and his government was committed to protecting the rights of dual citizens living within its borders.

Would Canada cancel pre-clearance?

No country would have more to lose from the cancellation of pre-clearance than Canada, if it is found that U.S. border agents enforcing the Trump visa ban are in violation of Canadian laws.

There are more pre-clearance points in Canada than in the other five pre-clearance countries put together, and more travellers pass through them.

Without such a system, the U.S. would have to put border agents in many more airports, or it would have to require all Canadian flights to land only at major international airports. Given the costs of the first solution, it seems likely the U.S. would opt for the second.

And so Canada has little incentive to bar U.S. border agents from Canadian airports.

Whatever conclusion the federal government comes to about the legality of the U.S. ban, any resident of Canada who feels he or she has been discriminated against at a Canadian airport has recourse to a Canadian court or to a human rights tribunal, which would then reach its own conclusion.

A ruling against the ban would potentially lead to a crisis over pre-clearance, since U.S. border agents would be obligated to enforce the ban, while Canadian law enforcement could be obligated to prevent them from doing so.