This story has been updated.

Nearly one month after President Trump declared the coronavirus a national emergency, and three weeks before he would like to reopen much of the country, the Food and Drug Administration has announced a comprehensive list of best practices to protect workers and consumers in the essential businesses that are feeding Americans during a pandemic when everyone is supposed to keep their distance.

Many of the guidelines reiterate practices already in place or considered a routine part of the food business — social distancing, no facial touching, standard food-safety procedures — but they also emphasize what companies should do to protect essential employees who may have been exposed to a co-worker with covid-19, but are at present asymptomatic. The FDA’s practices reiterate the new interim guidance from the Centers for Disease Control and Prevention, which has reversed its previous recommendations that workers exposed to someone with covid-19 (or even someone showing symptoms of the disease caused by coronavirus) should be sent home and quarantined for 14 days. There has been a labor shortage in the food retail industry, including supermarkets, which are trying to hire tens of thousands of workers.

If an employee turns up sick, the FDA and CDC are recommending a number of protocols to try to prevent the spread of the virus and avoid what happened at workplaces such as the Smithfield Foods processing plant in South Dakota, which was shut down this week after 80 employees were confirmed to have the coronavirus. The protocols include cleaning and disinfecting the work station of the infected employee; acknowledging that all employees within six feet of the infected worker have likely been exposed; and informing fellow employees of their possible exposure while maintaining confidentiality. Notably, the guidelines include contract workers, who are not considered formal employees, such as the drivers for food delivery companies.

But in a break with the CDC’s previous guidance, the agencies are not recommending that employees potentially exposed to the coronavirus be sent home and quarantined. Instead, the agencies recommend that employers assess the exposed workers’ health before they start a shift, including temperature checks. Potentially exposed employees should also wear masks, maintain six feet of separation from co-workers and assess their own health throughout the day.

The change in guidance has alarmed worker safety organizations.

“It is well established that there is significant risk of transmission from asymptomatic and presymptomatic individuals; thus these guidelines risk endangering workers, their families, their communities, and the public,” said Rebecca Dixon, executive director of the National Employment Law Project, in a statement.

“Essential workers in food processing, agriculture, janitorial, and many other critical industries are disproportionally [sic] workers of color, who are underpaid and already at increased risk of serious complications if they become infected with coronavirus,” Dixon continued. “With this new policy, the Trump administration has completely abandoned its responsibility to protect workers.”

The FDA is recommending that food workers wash their hands regularly and wear gloves at all times, while asking employers to discontinue “salad bars, buffets, and beverage service stations that require customers to use common utensils or dispensers.” The FDA is also encouraging retail stores to figure out ways to maintain six feet of space between customers in checkout lines or while waiting on a service. The agency is not recommending food workers wears masks unless they have been exposed to someone suspected of having covid-19.

Because the FDA’s authority is limited to food safety, the agency cannot require that restaurants, retail stores and other shops limit the number of customers who enter their establishments. These requirements must come from local jurisdictions or the Occupational Safety and Health Administration. This week, the D.C. government mandated that supermarkets, grocery stores, convenience stores, food halls and other establishments limit the number of customers to maintain six feet of separation between people. Montgomery County in Maryland issued a similar order, and other jurisdictions, such as the city of Miami, have mandated that shoppers wear face masks, as grocery chains are reporting their first employee deaths related to the coronavirus.

An FDA spokesman said the agency’s new guidelines were not a response to a letter Sen. Edward J. Markey (D-Mass.) sent this week. “We will respond directly to the Senator,” the spokesman, Peter Cassell, wrote in an email.

The senator’s Tuesday letter to the heads of the FDA and the CDC asked the agencies “to issue and promote clear guidance for workers in the retail food industry and their customers.” The senator said he was moved to action after an interaction with a supermarket worker who was “probably more exposed than almost anyone outside our medical community to hundreds of people a day, any one of which could have coronavirus.”

The latest FDA guidelines, however, are not mandates, which Markey would prefer to recommendations. They still leave safety decisions up to individual businesses.

“This overdue new guidance is an improvement from the minimal information FDA and CDC previously provided, but the Trump administration must do more to promote these resources to employers, employees, and consumers, and must ensure businesses are implementing these worker protections,” Markey wrote in a statement.

“Our frontline workers at grocery stores and in the retail food industry are making it possible for families and businesses to survive this pandemic, and we owe it to them to provide the resources they need to protect their lives and the public’s health.”

Correction: A previous version of this story said the Food and Drug Administration is recommending masks for all food workers. The agency is recommending masks only for workers exposed to someone suspected of having covid-19.

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