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More than two dozen Senate Democrats on Tuesday sent a letter to U.S. Agriculture Secretary Sonny Perdue raising concerns about the safety of keeping meat processing plants open during the coronavirus pandemic after President Trump late last month invoked the Defense Production Act (DPA) to help keep them open despite a spate of coronavirus cases among workers at such facilities.

The group of senators, which included moderates like Sen. Doug Jones, D-Ala., and hardline progressives like Sen. Bernie Sanders, I-Vt., and Sen Elizabeth Warren, D-Mass., said their interest in the topic was piqued by a Senate briefing in which USDA officials, according to the letter, were not able to confirm that newly reopened plants were following safety measures.

"We are concerned the Executive Order has put pressure on plants to reopen and that USDA is not taking sufficient measures to ensure the plants are operating consistent with federal safety guidance," the letter said. "[W]e understand that USDA officials could not confirm if the plants that reopened since the issuance of the Executive Order are operating in accordance with the CDC and OSHA guidance. They instead stated that it was their expectation that the plants were following the guidelines."

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Trump invoked the DPA late last month after hundreds of workers at meat processing plants tested positive for the virus, forcing some of the largest manufacturers in the business, which rely on thousands of people working side-by-side carving meat, to shut down or slow production. This caused worries that there could be a major meat shortage in the U.S., which Trump moved to allay with his DPA order.

"It is important that processors of beef, pork, and poultry ('meat and poultry') in the food supply chain continue operating and fulfilling orders to ensure a continued supply of protein for Americans," Trump's order said. "Such closures threaten the continued functioning of the national meat and poultry supply chain, undermining critical infrastructure during the national emergency."

The Democrats' letter cites numbers from the United Food and Commercial Workers International Union that at least 3,200 meat processing workers have been "directly impacted" by the coronavirus and that 35 workers had died as of May 12. It's unclear what "directly impacted" means in the context used by the Senate Democrats and the union.

Tyson Fresh Meats plant employees line-up outside of the plant, Thursday, April 23, 2020, in Logansport, Ind. The plant will temporarily close its meatpacking plant in north-central Indiana after several employees tested positive for COVID-19. (AP Photo/Darron Cummings)

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Concerns aren't just for the meat processing workers. The U.S. Department of Agriculture's Food Safety and Inspection Service (FSIS) told CBS News earlier this month that 145 employees were diagnosed with the coronavirus and an additional 130 are currently under self-quarantine as a precaution due to possible infection. The Democrats' letter asks Perdue how inspectors are being protected, and how the agency is preventing inspectors from carrying the coronavirus between facilities.

The Democrats noted that the Trump administration has said it would not issue any regulations or requirements based on the Trump DPA order, but pushed Purdue to strengthen that commitment.

"It is critical that you and the Administration clarify that nothing in the President’s Executive Order requires meat processing plants to stay open and the plants should only operate in accordance with the OSHA and CDC guidelines and any other requirements from state or local authorities," the letter reads.

It continues: "Additionally, we request that under the Executive Order, you ensure that all meat and poultry processing facilities operate in accordance with the OSHA and CDC guidance for meat and poultry processing employees and protect the workers from COVID-19 and that you institute a plan for monitoring and enforcement of that guidance."

The guidelines issued by the Trump administration address a broad variety of recommendations for meat processing facilities, including recommending that workers move in single-file lines, how to implement screening and the best sick leave policies to ensure sick employees don't come to work.

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The letter also asks several detailed questions on efforts to ensure meat processing plants are complying with federal rules and the Department of Agriculture's actions to protect workers, the supply chain and more.

The meat supply issues have triggered some outside-the-box thinking by other memers of Congress, too.

Rep. Thomas Massie, R-Ky., revived an old piece of legislation which would allow small farmers to sell meat directly to stores and restaurants -- making it easier for smaller farmers to contend with large conglomerates. Those large plants with thousands of workers processing meat on a massive scale are where the coronavirus outbreaks have happened.

"What this legislation would do is expand the exemptions and make it easier (for small farmers) to sell to places like grocery stores and restaurants," Massie, who first introduced the legislation along with Chellie Pingree, D-Maine, almost five years ago, told Fox News. "The same regulations that apply to multinational beef hackers that slaughter 10,000 animals a day shouldn't apply to a rancher slaughtering 20."

Fox News' Andrew O'Reilly, Hollie McKay and David Aaro contributed to this report.