Cases of COVID-19 have been confirmed at a third Alberta meat-packing plant, according to the union that represents those workers.

United Food and Commercial Workers Canada Union local 401 president Thomas Hesse said three cases of COVID-19 have been confirmed at the JBS plant in Brooks, Alta.

At the Cargill plant in High River, there are 38 COVID-19 cases, and in March one worker at Harmony Beef in Balzac tested positive.

Dedicated testing centre

Alberta chief medical officer of health Dr. Deena Hinshaw said while local health officials have resolved the situation at Harmony, the number of cases at Cargill have prompted Alberta Health Services to open a dedicated testing centre at that plant this week.

"Local public health has worked with these locations to ensure close contacts are isolated and prevent transmission. There is no risk to the public from food produced in these plants," Hinshaw said.

Hesse said the union has reached out to those plants — as well as Olymel pork plant in Red Deer — to request the companies proactively shut down to keep workers safe.

"They've all said no. But Cargill has in some ways, done what we've asked because of pressure," Hesse said, adding that the plant has reduced operations significantly.

Hesse said 1,000 workers at Cargill have been laid off and another 500 are without shifts.

But John Nash, the North American lead for Cargill Protein, said no layoffs are happening. Instead, he said a second shift at the plant has been cancelled and workers are being allowed to switch shifts if they are healthy and able to work.

Should Canadians be concerned about beef supply? A Cargill spokesperson says no, even with COVID-19 cases at three Alberta plants. 5:03

Nash said the plant is working with Alberta Health and its own safety officials, and will consider shutting down if necessary. Enhanced screenings, barriers between work stations and other physical-distancing measures have been put in place.

"If it comes to a point where we can't do what we need to do safely, we will not run that facility," Nash said.

A JBS Food Canada spokesperson confirmed its Brooks plant is staying open, and that workers have tested positive in some of its facilities.

"We are providing support to those team members and their families, and we hope they all make a full and speedy recovery. Out of respect for the families, we are not releasing further information," an emailed statement from JBS read.

The company said enhanced health and safety measures have been put in place.

"The food supply is a critical infrastructure industry and we have a special responsibility to maintain operations on behalf of the country. We take this responsibility seriously," the statement read.

Hesse said the plants are built to have workers in close quarters, making physical distancing challenging.

Roughly a dozen meat-packing plants in North America have shut down due to coronavirus.

The industry is a demanding one not withstanding the risk of infection due to close quarters, with workers subject to physical labour and repetitive tasks.

"Workers do work side-by-side ... crowded hallways, crowded locker rooms, crowded lunch rooms, crowded washrooms and of course a crowded production floor," Hesse said.

"This is a very profoundly unique time, and I just don't know why society is prepared to say 'stay home, do everything you can to prevent the spread of this virus' ... but we're allowing a free-for-all in food processing plants and grocery stores."

Those three plants represent roughly three-quarters of Canada's beef suppliers — Cargill alone, which supplies McDonald's Canada among others, accounts for more than one-third.

A cattle industry group has reached out to the federal government to ask that measures be put in place to slow the supply chain, as plants have to change operations to adapt.

If cases of COVID-19 continue to multiply, labour shortages could affect food supplies and undermine Canada's critical infrastructure, an internal government briefing note obtained by CBC News warns.

The document, prepared by Public Safety Canada, says accelerating rates of illness among Canadians could create labour shortages in essential services.

The two most "pressing" areas of concern, it says, are procurement of medical goods and the stability of the food supply chain.

Nash said Canadians should not be concerned about beef supply at this point but he said pressure to stay open will never lead to the company operating in an unsafe manner.