How will following those standards reduce legal risks?

If employers try in good faith to adhere to the standards, OSHA has said it will not cite the owner of a meat processing plant for operating an unsafe workplace.

Moreover, if sick workers or their estates file lawsuits claiming that they were exposed to the virus at work because of their employer’s negligence, following these standards will provide a defense in court: The Trump administration has offered to have a Labor Department official testify as a witness at trial that the federal government thinks the company was not at fault.

What did the Defense Production Act order do?

For now, nothing concrete. But it could repel any hypothetical future attempt by state officials to shut down a meat processing plant by imposing more stringent health and safety rules than the new federal guidance, and then accusing the facility of failing to live up to local standards.

The Defense Production Act permits the federal government to issue orders allocating where “scarce and critical material essential to the national defense” should go. The idea appears to be that Mr. Perdue could use this power to instruct a specific meat producer to allocate its product to grocery wholesalers in line with its existing contracts — thereby bestowing a federal gloss on those arrangements.

While some of the meatpacking plants have shut down voluntarily after outbreaks to clean their facilities, others have been ordered closed by local health officials. But those closures happened before the federal guidelines. Going forward, if state or local regulators created stricter rules, this maneuver could provide a basis to argue to a judge that the federal standards pre-empted the local ones.

How that would go is an open question. A 1950 ruling from a Federal District Court in Minnesota suggested that if there were a conflict with local rules, a Defense Production Act arrangement would prevail. But Mr. Baker noted that the act’s allocation powers “have not been used in a long time, nor have they been fully litigated.”

Still, he added, it might not be put to the test because there would also be pressures on all involved — the federal and state governments, companies and workers — to reach an accommodation rather than get mired in court.