TORONTO — Each summer for the past five years, Aaron has traveled from his home in Mexico to Canada as one of the tens of thousands of temporary foreign workers who seed, tend and harvest the crops that keep the country fed. This year's journey was different.

Flights were limited. There were temperature screenings and questionnaires before he took off and after he landed. On arriving in British Columbia this month, he checked into a hotel for a 14-day quarantine.

“I trust that everything will be fine,” said Aaron, a 31-year-old husband and father from Guanajuato state who spoke on the condition of anonymity.

But in this year of the novel coronavirus, the precautions have not kept all of Canada’s migrant farmworkers safe. At least 600 have contracted the coronavirus, and at least two, both Mexicans, have died.

Mexico, which provides nearly half of Canada’s migrant farmworkers, has become so concerned that officials said this week they’re hitting the “pause button” on plans to send up to 5,000 more to Canada until they’re satisfied the conditions that led to the deaths of Bonifacio Eugenio Romero, 31, and Rogelio Muñoz Santos, 24, will be rectified — threatening a labor crunch for Canada’s already squeezed agricultural sector.

“For us, it was only responsible to halt the coming of further workers until we have this clarity,” said Juan José Gómez Camacho, Mexico’s ambassador to Canada.

Mary Robinson, president of the Canadian Federation of Agriculture, said the loss of these workers would be “incredibly unfortunate” and would create “greater uncertainty, not only impacting this year’s harvest but next year’s cropping plans.”

The pandemic has highlighted Canada’s dependence on the 60,000 temporary foreign workers who arrive each year from countries such as Mexico and Jamaica as part of a federal government program, and without whom hundreds of thousands of tons of blueberries, asparagus stalks and grapes would wither on the vine.

They’re so vital that Prime Minister Justin Trudeau declared them essential workers, exempt from the restrictions that have shut the borders to most foreigners. They must quarantine for 14 days; Trudeau gave employers $37 million to cover those costs.

Trudeau said he offered condolences to Mexican President Andrés Manuel López Obrador.

“We should always take advantage of moments of crisis to reflect,” he said. “Can we change the system to do better?”

Advocates for migrant farmworkers have long criticized what they say are unfair and unsafe conditions in which many labor. Their work permits are often closed, binding them to one employer for a set term. That can leave them afraid to speak out about abuses, said Chris Ramsaroop, an organizer with Justice for Migrant Workers.

“Everybody in Canada knows about the injustices done to agricultural workers, and nobody has the guts to step forward to do the right thing,” he said.

During the coronavirus outbreak, advocates say, a lack of personal protective gear, no sick days, overcrowded living and working conditions and language barriers have put migrant farmworkers at a heightened risk for the coronavirus.

“The central problem is that workers don’t have power,” said Syed Hussan, executive director of the Migrant Workers Alliance for Change. “It’s an entire system of dehumanization.”

His group released a report this month detailing complaints by more than 1,100 migrant farmworkers during the outbreak. They included 40 workers sharing a single shower, sick workers not being isolated from the healthy and wage theft.

Under the Temporary Foreign Worker Program, farms are required to provide workers with affordable housing. Wajid Ahmed is the top doctor of largely rural Windsor-Essex County in southwestern Ontario, where some 340 migrant workers have tested positive for the coronavirus in eight separate outbreaks. He said the communal bunkhouses in which workers live are breeding grounds for contagion.

“When one person gets sick, and if they’re living with many other people in the same accommodation, it just spreads like wildfire,” Ahmed said. “That’s the biggest concern that we’re seeing.”

Officials have stressed that the migrant workers did not bring the virus to Canada but acquired it after the mandatory quarantine. In Windsor-Essex, outbreaks at farms are one reason provincial officials say the region cannot advance to the next stage of reopening.

“They came here, they self-isolated for two weeks and they picked it up since they’ve been here,” Ontario Premier Doug Ford said. “I don’t want any finger-pointing at these hard-working migrant workers.”

Advocates are calling for national housing standards, mass testing of workers and pathways to permanent residency.

“Anyone who does focused work with migrant workers knew this was coming, and so many of us were trying to raise awareness and alarm bells,” said Janet McLaughlin, a professor of health studies at Wilfrid Laurier University. “It just feels like people don’t heed warnings until tragedy strikes.”

Keith Currie, president of the Ontario Federation of Agriculture, said there were challenges obtaining personal protective gear in the early weeks of the pandemic, but the equipment is now “much more readily available.”

“We’re in never-before-seen times,” said Joseph Sbrocchi, general manager of Ontario Greenhouse Vegetable Growers, which represents some 220 cucumber, tomato and pepper farmers. “We didn’t have a playbook.”

Currie, whose farm in Collingwood, Ontario, grows grains, gladiolas and sweet corn, said some of the allegations about living and working conditions were “not true.” He said the “overwhelming majority” of employers treat their workers well and comply with rigorous standards.

“The foreign worker program for agriculture is some 50-plus years old,” Currie said. “Many of these employees are second and third generation, and you know, if they’re not treated well, why would they keep coming back?”

Aaron said some “bosses” abuse workers. When he finishes his quarantine, he’ll start work at a peach and apple farm in Keremeos, B.C.

“It is very difficult to come and do this work in the fields,” he said. “It is heavy, hard work in another country without the family. I miss my daughters, but it is a good opportunity.”

Gómez Camacho, the Mexican ambassador, said he is having “very fluid conversations” with Canadian officials: “We have to move fast.” Employment and Social Development Canada, the country’s labor ministry, said it takes his concerns “very seriously.”

It’s unclear how broad the Mexican pause is. Oscar Mora, a spokesman for the Mexican Embassy in Canada, called it a “general measure.” But a spokesman for Mexico’s labor ministry said it applies only to farms that have had outbreaks and “do not have a strategy for the protection and care of workers.”

“Workers who would have traveled to a farm where there is a health problem will be reassigned and will not lose the possibility of traveling to Canada and having an employment contract,” the spokesman said. He said the 26,400 Mexican workers who contracted with farms in Canada last year sent home remittances of nearly $250 million.

Rodrigo Tovar Esquivel, a coordinator for the Democratic Peasant Union in the Mexican state of Hidalgo, said the Mexican government has taken away support programs for farmers, pushing workers to seek opportunities elsewhere.

Alvaro López Ríos, head of Mexico’s National Agricultural Workers Union, said agricultural laborers “have so much lack of work that they accept anything.”

“They leave without thinking about the pandemic,” he said. “They leave thinking of having an income that they cannot obtain in Mexico.”

Romero and Muñoz Santos worked at different farms but died days apart, thousands of miles from family and friends.

Muñoz Santos did not travel to Canada as part of the Temporary Foreign Worker program. He came to Canada on a tourist visa in February, family members told the Mexican newspaper La Jornada, and then responded to an online ad from a farm in Ontario seeking workers.

McLaughlin, the Laurier professor, said their deaths represent “the tip of an iceberg of multiple levels of failure.”

Gómez Camacho said they were “very representative of what Mexican workers are in Canada.”

“They come here because they want to earn a salary, because they like the job, because they would like to provide for their families back home, because they believe Canada is a great opportunity for them.”

Martínez reported from Mexico City.