The uncertainty surrounding U.S. immigration policies has prompted a number of Canadian cities to declare themselves sanctuaries for undocumented migrants.

But as cities move to protect migrants from deportation orders, it is creating the prospect for tensions between municipal governments, law enforcement and federal immigration officials.

Montreal's city council voted unanimously on Monday to approve a motion that seeks to ensure non-status migrants are able to obtain municipal services without fear of being deported.

London, Ont., passed a similar motion last month — also unanimously — just days after the administration of U.S. President Donald Trump announced its travel ban on refugees and citizens from seven predominately Muslim countries.

People gathered earlier this month in Winnipeg to encourage Mayor Brian Bowman to pass a sanctuary-city motion. (John Woods/Canadian Press)

City councillors in Regina and Saskatoon have raised the possibility of passing their own versions of a sanctuary motion. Winnipeg, too, is considering following suit.

A municipal committee in Ottawa will hear from the public next month about whether to give itself the sanctuary city designation.

In 2013, Toronto was the first sanctuary city in Canada. Its city council passed a motion in January reaffirming its commitment to services and protection to undocumented migrants.

"No one should be made afraid because of who they are or where they come from," Mayor John Tory said at the time, criticizing the Trump travel ban.

Until Trump announced his plans for the sweeping ban, Hamilton (in 2014) and Vancouver (2016) were the only other cities to enact sanctuary provisions.

Co-operation of the police?

The immediate goal of these sanctuary motions is to allow migrants to obtain such municipal services as housing, libraries and food banks without being questioned about their immigration status.

More controversial, though, are stipulations that municipal law enforcement agencies limit their co-operation with federal immigration officials.

It is standard practice for many police forces in the country to share personal information, including immigration status, with the Canada Border Services Agency.

That means minor infractions, such as a traffic violation, can lead to deportation.

Advocates for non-status migrants say this discourages their clients from coming forward when they are witnesses or victims of a crime.

The immigration policies of the Trump administration have prompted Canadian cities to consider offering sanctuary to undocumented migrants. (Jeff Chiu/Associated Press)

As a result, some police forces have adopted "don't ask" policies. Police in Toronto, for instance, are trained to provide services without asking witnesses or victims about their immigration status.

Montreal's sanctuary motion calls for city and police officials to work out a policy that would achieve the same result.

More than symbolism

But these "don't ask" policies have been met with resistance from law enforcement and the federal government in the past.

When Vancouver's transit police announced in 2015 they would adopt a don't ask policy, then immigration and citizenship minister Chris Alexander criticized the decision.

"Canadians have told us that they have no tolerance for those who use fraudulent means to enter Canada, and abuse Canadian generosity," Alexander said in a statement at the time.

A recent study of Toronto's sanctuary provisions found police applied the "don't ask" policy unevenly.

And when the city reaffirmed its commitment to being a sanctuary city last month, Deputy Mayor Denzil Minnan-Wong was conspicuously absent for the vote. He later tweeted.

I support legal immigration. I do not support illegal immigration. We have laws. They should be followed. —@DenzilMW

But for those who advocate for non-status migrants, co-operation by the police is essential if sanctuary motions are to be more than mere political symbolism.

"A lot of things are not clear about how it would work," said Jenny Jeanes, a co-ordinator with the refugee advocate group Action Réfugiés Montréal, about the motion passed by Montreal's city council.

"For it to be actually meaningful the police somehow have to be involved."

CBC News was not able to reach a representative of the Liberal government for comment on Monday.

The Canada Border Services Agency did not respond to a request for information about its relationship with Montreal police. Montreal police also did not respond to a request for comment.