OTTAWA -- The federal government has been warned to take a cautious approach to publicly debating immigration over fears of reaching a "tipping point" that could undermine public support for welcoming immigrants.

Internal data prepared by the Immigration Department for a committee of deputy ministers suggests a majority of Canadians supports current immigration levels, but this support drops when they are informed of how many immigrants actually arrive every year.

"Public support (often aided by a diversity of prominent stakeholders) in indispensable," the department told the co-ordinating committee of deputy ministers during a meeting in April 2017 to discuss immigrant outcomes.

"But there could be a tipping point that, once reached, undermines the history of relative Canadian consensus."

The internal departmental data was obtained by The Canadian Press through access-to-information. It includes polling data that suggests just over 50 per cent of Canadians believed the number of immigrants who come to Canada every year is "about right" and this number has remained steady since 2012.

But most of those respondents believed the number of immigrants arriving every year was under 150,000. After they were told is has actually been 260,000 for the last few years, the number of people who then said they felt that was "too many" jumped from 23 to 32 per cent.

Global events affect opinions on immigration, notably the drowning of three-year-old Syrian refugee, Alan Kurdi, in 2015. Other circumstances can also colour public attitudes, including hardening attitudes toward immigration in other countries and feelings of disenfranchisement as a result of economic downturns, the department noted.

"Engagement with the Canadian public is necessary, however, any high-profile debate will have to be carefully managed," the department advised.

Keith Banting, research chair on public policy at Queen's University, has studied Canada's changing perception of multiculturalism policies. He's seen a growth in overall support for current immigration levels, especially when compared with historic data.

But when it comes to increasing the number of immigrants, opinion becomes more divided.

"About 30 per cent of Canadians think immigration levels are too high ... There's a cluster of people who are simply opposed. At the other extreme, there's another group who are super keen," Banting said.

"In the middle, are what we call the conditional multiculturalists. They are, in principle, comfortable with (immigration) but subject to a whole set of qualifications which really turn on whether it is working."

Given this complexity of opinions, it is possible to mobilize and shift public opinion in favour or against the idea of immigration, Banting said.

The government released its three-year immigration strategy late last year which plans for incremental increases to immigration levels over the next three years. But many immigration advocates and economic groups, including the federal government's own economic advisory council, had called for more significant increases.

Banting said he believes government chose a more measured approach due to fears of public "backlash."

Immigration Minister Ahmed Hussen's press secretary, Mathieu Genest, told The Canadian Press the government's three-year immigration plan was developed after hearing feedback from consultations held across the country.

"We are certain that we have a vision that Canadians believe in," Genest said.