On Aug. 22, hours before Vice President Kamala Harris took the stage in Chicago at the Democratic National Convention, Donald Trump was claiming that she would abolish Immigration and Customs Enforcement and allow more than 100 million people to cross into the United States. “If Comrade Harris has the chance,” Mr. Trump warned from Cochise County, Ariz., on the U.S.-Mexico border, “our country will be overrun and essentially it won’t be a country. It will be not governable.” He then renewed his promise to use the military and other government resources to arrest and banish millions of immigrants living in the United States, including those in various humanitarian programs. “With your vote,” Mr. Trump said, “we will seal the border, stop the invasion and launch the largest deportation effort in American history.”

It would be easy to dismiss these threats as posturing to stir up his base, but recent reporting suggests that Mr. Trump’s allies are drawing up plans for the most regressive immigrant policy since 1954, when Dwight Eisenhower’s administration rounded up as many as 1.3 million people, mostly Mexican and Mexican American workers, as part of the openly racist campaign known as Operation Wetback. According to reporting by The Times and The Wall Street Journal, Mr. Trump’s plans — which he describes as “following the Eisenhower model” — would not just remove people already in the United States but also cut off the flow of new migrants. If carried out abruptly and thoroughly, as Mr. Trump has promised, such policies would threaten vital areas of the American economy dependent on immigrant labor. Nowhere is that more evident than in the meat industry.

Not so long ago, America’s meatpackers relied heavily on undocumented immigrants from Mexico and other Latin American countries to staff their factories. But a brutal set of government raids in 2006 changed their calculus. On Dec. 12 of that year, I.C.E., newly created by President George W. Bush, simultaneously entered six Swift & Company meatpacking plants and arrested 1,300 undocumented workers on charges of immigration violations and identity theft. In the tiny town of Cactus, Texas, agents barred the plant doors and began handcuffing workers. “There were people hiding behind machinery, in boxes, even in the carcasses,” an employee later told The Washington Post.

In Cactus alone, nearly 300 employees, about 10 percent of the town’s population, were arrested. When agents ran out of handcuffs, they tied workers with rope. It was the largest workplace immigration raid in American history. At the time, the I.C.E. director, Julie Meyers, said, “The action should send a clear message to employers: Hiring illegal workers is not acceptable.”

The raids appeared to have their intended effect, and meatpackers soon began seeking out a new class of vulnerable foreign workers: refugees here legally, as well as immigrants who either walked across the border and are allowed to stay for humanitarian reasons or are seeking asylum. Today, nearly half of the people who slaughter, butcher and package beef, pork and poultry in America were born elsewhere. In some packing houses, more than four dozen languages are spoken. In some, Somali, Sudanese and Burmese refugees alone account for as much as a third of the work force. The fact is, America’s largest meat producers are dependent on the immigrants Mr. Trump is threatening to round up and deport.

If he is elected and makes good on his promise to bar refugees, those producers could lose a vital source of labor overnight. If he succeeds in rescinding certain protections for asylum seekers and speeds the process of deportation trials, the entire industry could be brought to a halt. Meat processors are only just recovering from the ravages of the pandemic. This would push them to the breaking point — and perhaps crash the whole food system.