“They are being aggressive and trying to target rogue H.R. managers or others within the management chain,” said Ms. Wood, who is now the chief executive of Guidepost Solutions, a compliance firm.

She said it was difficult to prosecute companies for hiring undocumented workers, as significant evidence would be needed to prove complicity.

Prosecutions are not common, said Kimberley Best Robidoux, a business immigration lawyer in San Diego who specializes in compliance. According to data compiled by Syracuse University and released in May, only 11 people were prosecuted from April 2018 through March 2019 for employing immigrants who did not have proper documentation. No companies were prosecuted during that time, according to the data.

The raids on Aug. 7 were the largest to occur since President Trump, who has made illegal immigration a focal point of his presidency, took office.

According to the affidavits, the Peco Foods plants targeted in the raids are in Bay Springs, Canton and Walnut Grove; The Koch Foods plant is in Morton, as is the P H Food Inc. plant; The Pearl River Foods plant is in Carthage; and the A&B Inc. plant is in Pelahatchie.

The United States Attorney’s Office for the Southern District of Mississippi, which conducted the searches with ICE, said that some of the people who were rounded up were taken to an ICE detention center in Jena, La. Others have been released on “humanitarian” grounds, but they are required to appear before a federal immigration judge who will determine whether or not they will be deported.

The affidavits outline previous arrests of undocumented workers at the plants. For example, from September 2002 to April 2019, there were 144 arrests or encounters with undocumented immigrants who said they were employed at Koch Foods plants in Morton or Forest.