(usat) Federal immigration agents today raided the nation's largest kosher slaughterhouse and meat-packing plant and arrested more than 300 people in northeastern Iowa. Most are accused of identity theft and of being in the country illegally. The Des Moines Register (a Gannett newspaper) reports that according to search warrants unsealed today, federal authorities had received information about alleged immigration violations for the past two years at Agriprocessors Inc. in Postsville. One source, a former plant supervisor, told agents the plant hired foreign nationals from Mexico, Guatemala and Eastern Europe. Around 80% were in the United States illegally, said a supervisor with U.S. Immigration and Customs Enforcement. The source also reported that some employees were running a methamphetamine lab in the plant and were bringing weapons into the plant, which employs about 1,000. He said he was fired after he told his superiors. Authorities have released about 40 workers, with supervision, “on humanitarian grounds” because they are primary care-givers. The National Cattle Congress fairgrounds in nearby Waterloo is being used as detention center. The Waterloo-Cedar Falls Courier says the community heard Friday about the impending raid, the largest in Iowa history. When the raid began this morning, family members of plant workers headed to St. Bridget’s Catholic Church, a few blocks away. “The people right now are hearing and seeing the helicopters,” Sister Mary McCauley told the Associated Press. “They are just panic-stricken and very frightened and some of them are coming to the church as a safe haven.” So far, Agriprocessors has declined to comment. The company's products can be found nationwide in Wal-Mart, Trader Joe’s, Albertson’s and Kroger, among others. On its Web site the company says it "strives to be second to none in producing the finest quality beef and poultry products at a reasonable price. We are devoted to our customers and are committed to following and upholding the federal, state, and local laws and regulations governing our business.