"Such closures threaten the continued functioning of the national meat and poultry supply chain, undermining critical infrastructure during the national emergency. Given the high volume of meat and poultry processed by many facilities, any unnecessary closures can quickly have a large effect on the food supply chain. For example, closure of a single large beef processing facility can result in the loss of over 10 million individual servings of beef in a single day. Similarly, under established supply chains, closure of a single meat or poultry processing facility can severely disrupt the supply of protein to an entire grocery store chain.

Accordingly, I find that meat and poultry in the food supply chain meet the criteria specified in section 101(b) of the Act (50 U.S.C. 4511 (b)). Under the delegation of authority provided in this order, the Secretary of Agriculture shall take all appropriate action under that section to ensure that meat and poultry processors continue operations consistent with the guidance for their operations jointly issued by the CDC and OSHA. Under the delegation of authority provided in this order, the Secretary of Agriculture may identify additional specific food supply chain resources that meet the criteria of section 101(b)."

Meat and Poultry Processing Workers and Employers
Interim Guidance from CDC and the Occupational Safety and Health Administration (OSHA)

https://www.cdc.gov/coronavirus/2019-ncov/community/organizations/meat-poultry-processing-workers-employers.html