The number of COVID-19 cases linked to meat-processing giants Tyson Foods, Smithfield Foods and JBS has nearly quadrupled over the past month from about 3,000 to more than 11,000, a Washington Post analysis found.

The virus had killed at least 64 workers across the industry as of Tuesday, according to the Midwest Center for Investigative Reporting, which is using local news reports to track deaths. That’s more than triple the 20 fatalities the Centers for Disease Control and Prevention recorded in April.

The reported spike came as meat producers worked to shore up the nation’s food supply chain by restarting plants that were shuttered by coronavirus outbreaks. Such shutdowns have led to shortages of beef, pork and chicken and forced farmers to euthanize animals.

More than half of the 30 plants closed by the virus have reopened over the past month amid President Trump’s April 28 executive order directing them to get up and running, according to the Washington Post.

But producers have reportedly drawn fire for shortchanging worker safety in the process despite their efforts to keep plants clean and prevent staffers from getting sick.

“We are raising hell because the numbers continue to rise,” Kim Cordova, a local union president in Greeley, Colorado, told the Washington Post. “People are scared to go to work because people keep getting sick. There are hundreds of workers who have not come back.”

Greeley is home to a beef plant run by Brazilian processor JBS, which told the paper that it’s made more than $100 million worth of safety enhancements at its facilities, from temperature checks to masks and face shields. Fellow producers Tyson and Smithfield also reportedly say they’ve taken big steps to protect workers.

“The safety of our team members is paramount, and we only reopen our facilities when we believe we can safely do so,” Gary Mickelson, director of media relations for Tyson, told the Washington Post.