Federal authorities apparently had a good reason for conducting one of the biggest immigration raids in a decade this past week.

Six of the seven Mississippi food plants that got hit by ICE agents on Wednesday were “willfully and unlawfully employing illegal aliens” — with many working under false names and fake Social Security numbers, according to investigators.

Documents unsealed Friday by the US Attorney’s Office for the Magnolia state’s Southern District outline how authorities worked with confidential informants over the span of a year to uncover the use of ineligible employees.

Supervisors allegedly turned a blind eye to unlawful practices, such as hiring the same workers repeatedly under various names and not checking whether they had the proper paperwork.

To add insult to injury, some of the plant owners were embezzling money by adding other fake names and social security numbers to their payroll and keeping the cash they purportedly made for themselves, authorities say.

An employee at one plant, owned by PH Food Inc., told Homeland Security investigators that nearly all of its 240 workers in Morton, MS — as well as some 80 employees at an A&B plant in Pelahatchie — had been hired illegally. Many of them were allegedly from Guatemala.

“Food, Inc. and others are willfully and unlawfully employing illegal aliens in violation of Federal Law,” authorities allege in the federal documents.

“The payroll companies, as well as PH Food Inc. and A&B Inc. do not verify the authenticity of their documents,” said one informant.

Mississippi employers are required by state law to check documents using a voluntary online federal database system known as E-Verify.

A company behind one of the food processing plants targeted on Wednesday — Peco — said it uses E-Verify and “adheres strongly to all local, state and federal laws.” Attempts to reach A&B and PH Food were unsuccessful.

Koch, another company that owns one of the plants, said Friday that it relies on a “strict and thorough employment verification policy.” It told the Associated Press that no managers or supervisors had been arrested. It’s unclear if anyone from any of the companies involved has been charged, for that matter.

Nearly 700 workers were detained during the immigration raids, which were conducted by the Immigration and Customs Enforcement agency. Three hundred of them have since been released.

President Trump on Friday praised ICE for the roundup, saying it served as a strong deterrent to illegal immigration.

“I want people to know that if they come into the United States illegally, they’re going to be brought out. And this serves as a very good deterrent,” the president said. “If people come into our country illegally, they’re going out. They’re not coming in illegally and staying.”

With Post wires