Federal officials say a raid at a northeastern Iowa meat processing plant this week was the largest in U.S. history, in terms of the number of people arrested.

Immigration and Customs Enforcement officials say 390 people have been arrested on immigration charges after Monday’s raid at Agriprocessors Inc. in Postville, the world’s largest kosher meatpacking plant.

The plant and the town of Postville have drawn national attention in recent years because the plant is owned by the Rubashkin family, who are members of the Lubavitch sect of Hasidic Jews, who  live in strict compliance with commandments in the Torah. The laws dictate their dress, prayer, study, diets and gender roles.

Their operation of the Kosher meat plant in Postville was documented in a 2000 book, "Postville: A Clash of Cultures in Heartland America," by  Stephen Bloom, a journalism professor at the University of Iowa.

The Rubashkins also own a meat processing plant in Gordon, Neb., Local Pride, operated in cooperation with the Oglala Sioux tribe of South Dakota.  There was no raid on that plant, the Associated Press reported. 

Bloom's book documents how, except in the course of business, the Postville Hasidim largely kept to themselves, which did not sit well with some residents who made efforts to reach out.

The Rubashkins have faced labor shortages in Postville, which attracted other immigrants to the area, including non-English-speaking Eastern Europeans and Hispanics.

The raid this week was aimed at seeking evidence of identity theft, stolen Social Security numbers and people who are in the country illegally, authorities said.

Fifty-six of those arrested have been released on humanitarian grounds,  many of them to take care of children, the Associated Press reported.

The hundreds of people arrested were held in local jails or driven by bus about 75 miles to the National Cattle Congress fairgrounds in Waterloo. Federal authorities previously leased the fairgrounds and have turned it into a secure center.

According to an affidavit and search warrant, authorities relied heavily on an informant who infiltrated the plant with documents provided by the Immigration and Customs Enforcement agency.  The informant was hired in January and wore recording devices monitored by ICE, according to the Associated Press.

The informant allegedly witnessed a system in which some employees were paid in cash or with checks that did not have Agriprocessors' name on them.

 Matt M. Dummermuth, U.S. attorney for the Northern District of Iowa, said the raid came after months of planning, beginning in October. Federal agents were helped by state and local police.

The raid was reminiscent of the December 2006 immigration raids at Swift & Co. meatpacking plants in Iowa, Nebraska and four other states, that were criticized by immigrants’ advocates.

Asked if Monday's action differed from previous raids, officials said no.

  “We're doing things the way we always do,” said Claude Arnold, special agent in charge of ICE's office in Bloomington, Minn.  “We're doing things the right way.”