Authorities arrested Thursday 2 supervisors from a kosher meatpacking plant in Iowa. They were accused of helping illegal immigrant workers hide from authorities by using fake Social Security numbers.

According to The New York Times, prosecutors said that Juan Carlos Guerrero Espinoza and Martin De la Rosa Loera were arrested on criminal immigration charges. They worked at the Agriprocessors plant in Postville. The two supervisors helped illegal immigrants to work at the plant. Apparently authorities were searching for a third man who was believed to be the plant manager. Hosam Amara, 43, was a floor manager and had more authority that the other two men.

The arrest happened after federal authorities conducted an immigration raid on May 12. It was the largest immigration raid at a single workplace in the history of America, as authorities arrested about 389 illegal immigrant workers, reported Bob Teig, a spokesman for the United States attorney for the Northern District of Iowa.

Martin De la Rosa Loera was in charge of the plant’s poultry kill facility and Juan Carlos Guerrero Espinoza was in charge of the beef kill and he is a U.S. citizen, said Assistant U.S. Attorney Pete Deegan, according to Gazette Online.

Agriprocessors is the country’s biggest producer of kosher meat and his owner is Aaron Rubashkin.

Most of the workers who were arrested were from Guatemala. About 270 workers were sent to federal prison on criminal charges. According to the complaint, the workers said that Juan Carlos Guerrero Espinoza told them they had to get new IDs and Social Security numbers in order to continue their work at the plant. Each of the workers gave Juan Carlos Guerrero Espinoza $200 and a photograph who said he would make sure they receive the new documents.

Scott Frotman, a spokesman for the United Food and Commercial Workers Union said authorities had to dig deeper and find all the guilty persons.

“What about the allegations of worker abuse? Does anyone really believe that these low-level supervisors acted alone without the knowledge, or even the direction, of the Rubashkins and other senior management?” said Scott Frotman, according to The New York Times.

The two supervisors were in the custody of U.S. marshals and they were scheduled to appear on court Monday.