The world's biggest meat companies, including Smithfield Foods Inc, Cargill Inc, JBS USA and Tyson Foods Inc, have halted operations at about 20 slaughterhouses and processing plants in North America as workers fall ill, stoking global fears of a meat shortage.

US President Donald Trump on Tuesday invoked the Defense Production Act to mandate meat plants continue to function during the pandemic after companies warned of looming shortages. The order is designed in part to give them legal cover with more liability protection in case employees catch the virus as a result of having to go to work.

"There is plenty of protein in the supply chain. However, some processors are experiencing challenges," a Kroger spokesperson said.

COVID-19 cases at a JBS meatpacking plant in Colorado have more than doubled "in a number of days" and a sixth employee died of the virus, a union official said on Thursday (30 April), underscoring the risks of US meat plants reopening.

The plant in Greeley, Colorado, started operating last Friday after it was closed for about two weeks following an outbreak among workers.

"The uptick in cases in a matter of days shows how serious this crisis is and the dangers that workers are facing every day just trying to do their jobs," Kim Cordova, leader of the local United Food and Commercial Workers International Union chapter, said in a news release.

Confirmed cases among workers at the plant rose from 120 on Sunday to 245 on Wednesday evening (29 April), a union spokeswoman told Reuters, citing numbers from the Colorado Department of Public Health and Environment.

The news of the purchase restrictions was first reported by CNN, and the report added Walmart Inc does not expect it will have to set product limits on meat.