Workers at the Worthington plant say they expected the raid. The Swift plant employes more than 2,000 people.
"About seven or eight guys come around me and they're asking me what am I doing, if I got papers, which I do," a Swift employee told Minnesota Public Radio. "So I showed them proof of that and they just kept asking questions, like if I have weapons or what I was doing there."
The man, who didn't want his identity revealed, says he expects that hundreds of people could be arrested. He guesses half the workers in the plant may be illegal.
As he spoke, more than a half-dozen federal buses arrived to transport suspects. Officials with U.S. Immigration and Customs Enforcement -- ICE -- says the Worthington raid was part of a 10-month investigation of an identity theft ring.
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Tim Counts, with the Minnesota ICE office in Bloomington, says he has no idea how many people will be taken away.
"This whole operation has been very methodical, very studied and we have asked Swift managers to shut down various portions of the processing, one at a time, so that we could interview the employees working in those areas," says Counts. "So it's kind of a slow ongoing process. But as soon as we have everbody interviewed, we'll get out of the way and allow Swift to get back to work."
Counts says the agents' mission is to apprehend every illegal immigrant in the plant.
"The ICE action was totally uncalled for," said Jim Papian, with the United Food and Commercial Workers Union, which represents the Swift workers. "This is scapegoating. This is the result of scapegoating workers who go into the plants everyday. They work hard, they help their companies become successful. They contribute to their communities. This really is about a totally broken-down immigration system; an immigration system that is in tatters -- an immigration system that was built for the 19th century, not the 21st century."
Papian says the union will seek federal court help to stop the arrests. ICE representative Tim Counts says the action was necessary to fight a growing wave of illegal immigrants involved in identity theft.
"In this particular case, we've done something that we don't typically do and that is work with the Federal Trade Commission," said Counts. "They are the ones who have identified several hundred U.S. citizens and legal immigrants who may have been victimized by people working at these Swift plants."
Counts says the illegal immigrants may have used stolen Social Security numbers to get hired by Swift. Union officials see suffering on their side as well, they plan to set up assistance centers for Swift employees needing help.
No charges had been filed against the company. "Swift has never condoned the employment of unauthorized workers, nor have we ever knowingly hired such individuals," Swift & Co. President and CEO Sam Rovit said in a statement.
Since 1997, Swift has been using a government pilot program to confirm whether Social Security numbers are valid. Company officials have previously said one shortcoming may be the program's inability to detect when two people are using the same number.
(The Associated Press contributed to this report.)