Canada's reputation as an open society risks being tarnished after many invitees to the World Social Forum 2016 in Montreal had their visitor visa application denied by the government, organizers said Monday.

Twenty-four hours before the beginning of the international event, conference co-coordinator Raphael Canet told reporters the number of people denied entry to Canada hasn't changed much since he raised the issue a week ago.

Canet said he sent 2,000 letters of inquiry to conference invitees asking about their travel plans and 70 per cent of the 315 people who replied said their visa application had been rejected by the Canadian government.

Co-organizer Carminda MacLorin said Canada's reputation as a free and open society will be "tainted" if there are fewer people at this year's conference.

The majority of the people denied entry visas are from Africa, and many are from Latin America, organizers said.

Immigration Canada blamed conference officials and said rules for visitor visas need to be followed rigorously, while the event's directors said they did all they could to facilitate the visa process.

World Social Forum is an annual conference that is being held in North America for the first time. It brings together left-leaning activists and other international civil society organizations, although most of the attendees are usually from the host nation.

Topics of discussion this year include "alternatives facing the capitalist crisis," "workers against neoliberalism," and the "struggle for justice and demilitarization," according to the event's website.

Organizers say roughly 15,000 people have registered for the six-day event, which begins Tuesday.

The conference has been widely criticized by Jewish groups claiming the event offers a platform to anti-Israel speakers advocating an international boycott of the country.

Moreover, the Toronto-based Jewish Defence League announced it would be present in Montreal to protest outside an event Wednesday that discusses how churches can join the Israel boycott movement.