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Some of the leading artificial intelligence experts from Africa and South America have been denied visas to attend a major industry conference in Canada, dealing a setback to efforts to prevent bias from taking root in the new technology.

Conference organizers say Canadian immigration authorities have denied visas to two dozen academics from countries such as Nigeria and Brazil, preventing them from attending the event next month in Vancouver.

Katherine Heller, a professor who serves as co-chair of diversity and inclusion at the Neural Information Processing Systems conference, said organizers “are trying extremely hard” to have the visa denials overturned.

“It is very significant for the field of AI that all voices be heard,” she said.

The problem of algorithmic bias in data science has become more pronounced, and there’s mounting evidence that AI-powered algorithms display bias against women and some racial groups.

Data-driven systems replicate patterns in society and are therefore at risk of bias, said David Leslie, an ethics fellow at The Alan Turing Institute in the United Kingdom.

“When you’ve got systems standing in for people, you want as diverse and inclusive a bunch of people designing those systems,” Leslie said.

Twenty-four researchers from Africa and South America who were scheduled to attend a Black in AI workshop at the conference had visas refused, workshop organizer Victor Silva said. Forty applicants from the two continents have been granted visas, but more than 70 applications are still pending, he added, less than a month before the conference is due to begin.

Black in AI sponsor companiessuch as Google (GOOGL), Microsoft (MSFT) and IBM (IBM) had offered to cover trip expenses for participants in the workshop, Silva told CNN Business. He said the researchers include “the best in their field around the world.” Some had already had to book flights as a condition of their visa applications, he added.

It’s the second year running that visa denials have prevented some African researchers from attending the conference, which was held last year in the Canadian city of Montreal.

Heller said there is already a contract in place to host next year’s conference in Canada, but the event is unlikely to be held in the country if attendees are denied visas for 2019.

Tejumade Afonja, a Nigerian who is studying for a Masters in computer science in Germany, posted her visa rejection letter on Twitter. She is one of the organizers of a workshop on machine learning for the developing world.

The letter, sent by the Canadian embassy in Vienna, Austria, said the embassy was “not satisfied” that Afonja would leave Canada at the end of her stay based on her travel history, immigration status and reason for visiting.

CNN Business was not able to verify the authenticity of the letter.

A spokesperson for Immigration, Refugees and Citizenship Canada said the department cannot comment on particular cases but that all visitors to Canada must meet the requirements for temporary residence, as set out in Canada’s Immigration and Refugee Protection Act.

These include being able to demonstrate sufficient ties to their home country and the means to support themselves while in Canada. Other factors, such as the overall economic and political stability of the home country, are also considered.

“All applications from around the world are assessed equally against the same criteria,” the spokesperson said, adding that conference organizershadregistered the event with the department in May, and shared lists of attendees on October 21 and November 2. This information was shared with visa offices assessing the applications abroad, the spokesperson added.

Canadian Prime Minister Justin Trudeau told WIRED last year that he would look into why more than 100 African AI researchers had been barred from visiting Canada for last year’s conference. His office did not respond to a requestfrom CNN Businessfor comment.

Academics from emerging economies face barriers

The situation highlights the barriers that academics from certain countries face when traveling to Western countries that require visas, which are often costly and administratively onerous.

Adarsh Jamadandi, a research assistant at India’s KLE Technological University, told CNN Business that he was also refused a visa on the grounds that he did not have a “legitimate business purpose” in Canada and might not leave the country. He was due to present research.

Sukaina Ehdeed, a Libyan academic currently doing a PhD at the University of Sheffield in the United Kingdom, said she has twice been denied visas to Canada to present research.

“When your visa applications to attend academic conferences get routinely denied, you lose any enthusiasm for ever responding to a call for abstracts,” she wrote in a recent blog post for the London School of Economics, adding that she did not submit work to a conference in the United States this year due to President Donald Trump’s travel ban against citizens from seven countries, including Libya.

A Libyan passport is one of the worst passports to hold, allowing visa-free access to just 37 countries worldwide, according to the Henley Passport Index, which also scores Lebanon, Nepal, Somalia, Syria, Pakistan, Iraq and Afghanistan among the lowest in a ranking of passports. European countries dominate the list of the world’s best passports to hold in 2019.