On Thursday in Montreal, Canadian prime minister Justin Trudeau boasted about his country’s leading position in artificial intelligence and openness to international collaboration. A few miles away, the world’s largest AI conference proceeded without scores of researchers denied visas by Trudeau’s government.

All week, Montreal has played host to 8,000 people attending the NeurIPS conference, which ends Saturday. But well over 100 researchers with tickets to attend the event or its associated workshops, including many who planned to present work, are absent due to visa denials or delays.

AI researchers say the visa problems undermine efforts to make their field more inclusive, and less likely to produce technology that discriminates or disadvantages people who aren’t white or Western. Scores of people due to attend or present work at Black in AI, a workshop that took place Friday, were unable to travel to Canada. Many were coming from African countries.

“We’re trying to democratize AI so it works for all people, not just some,” says Rediet Abebe, a grad student at Cornell who one is of the event's organizers. “The process to apply for Canadian visas has been very difficult for many people.” That’s a worry not just for this year’s conference, but because NeurIPS for the next two years will be held in Vancouver.

The problems faced by some would-be attendees stand in contrast to Trudeau’s championing of Canada’s openness to talented immigrants. On a visit to Silicon Valley in February, Trudeau touted a program introduced by his government that allows skilled workers to get a work visa in just two weeks. Facebook and Samsung have opened AI labs in Montreal in recent years.

When WIRED asked Trudeau at a G7 conference on AI about the visa challenges Thursday, he said it was the first he’d heard of the issue, and defended his government’s policies. “I can assure you that Canada is world-class in the way that it approves visas and encourages people from around the world to come participate in important global conversations like these,” he said.

Trudeau added that he wanted to learn from the problems: “I'm sure that there will be people looking into what you have described.”

Google’s top AI executive, Jeff Dean, previously had appealed to Trudeau via Twitter to help people struggling to gain visas for NeurIPS, but his message received no public reply.

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At the Black in AI event Friday, one room featured recruiting booths from event sponsors Amazon, Google, IBM, and Intel. In the next room, one wall was lined with more than a dozen shiny new laptops, so that researchers unable to travel could offer short, interactive presentations on new research via video chat. Organizers had expected a handful of remote presenters, but ended up with more than 40.

Research presented at the workshop covered highly technical topics including recurrent neural networks, finite automata, and how to get machines to detect early signs of breast cancer.

The visa problems prompting complaints at NeurIPS appear to reflect long-standing challenges for people from certain countries, particularly African, in traveling to Canada. El Mahdi El Mhamdi, a grad student at the Swiss Federal Institute of Technology in Lausanne and native of Morocco, tweeted that past visa hassles had convinced him not to bother attending NeurIPS.

The visa problems were not limited to one global region. Chip Huyen, a researcher at chipmaker Nvidia based in Silicon Valley, asked a colleague to give her talk about an open source software package for machine learning. A Vietnamese national, she didn’t hear back from Canadian visa officials in time to travel to Montreal. Since President Trump enacted his “travel ban” last year, some Iranian researchers in the US have been wary of traveling for fear of not being able to return home.