WASHINGTON (CNN) -
Federal officials raided Wal-Mart stores across the United States Thursday, arresting about 250 illegal immigrants working on cleaning crews at 61 stores in 21 states.
Federal agents picked up undocumented workers from Mexico, eastern Europe and other countries who were employed by several contractors used by the world's largest retailer. Many of those arrested in the crackdown, which officials called "Operation Rollback," were coming off night cleaning shifts at various Wal-Mart stores.
Garrison Courtney, a spokesman for the Bureau of Immigration and Customs Enforcement (ICE), said the raids started at 4 a.m. ET and ended about five hours later.
A search warrant also was executed at Wal-Mart headquarters in Bentonville, Ark., Courtney said, but he declined to provide details on what investigators were looking for or what they actually found.
"We are always looking at companies that are knowingly exploiting people for the purpose of making money," Courtney said. He said businesses that employ undocumented workers often pay low wages and offer few or no benefits.
"We're currently trying to understand the scope and the detail of the investigation," Wal-Mart spokeswoman Sharon Weber told CNN. "We are talking to the [immigration bureau] and, of course, are committed to cooperating with them."
Wal-Mart uses at least 100 outside contractors for cleaning services at about 700 stores across the country, she said. "We do require each of these contractors to use only legal workers. We do not know if the current investigation involves one or multiple outside contractors," Weber added.
None of the people arrested were Wal-Mart employees hired by the company to work in its stores, she said.
But federal law enforcement officials said information from an undercover investigation revealed that some Wal-Mart executives and some store managers knew of the immigration violations.
Some of the information in the investigation was gathered through the recording of conversations between store managers and contractor executives, the officials told CNN.
Investigators are concerned that Wal-Mart has kept using contractors who have been convicted of hiring illegal workers in the past. The latest sweep stemmed from a 1998 investigation that also targeted janitorial contractors at Wal-Marts, federal sources said.
Courtney said the penalty for knowingly hiring illegal workers can run up to $10,000 per person. He declined to give the names of the contractors who hired the workers picked up Thursday.
"People have to be authorized to work in the United States," said Courtney. "We are serious about enforcing the law."
The arrests on immigration violations involved no criminal charges. But sources said grand jury subpoenas have been issued in an ongoing investigation that could potentially result in criminal charges.
Industry analysts said the probe might hurt Wal-Mart's image but wouldn't necessarily hurt its financial results.
"It looks like these illegal workers were hired by contractors and not directly by Wal-Mart. Is this really bad press or slightly bad press? I think it's the latter," said Mark Mandel, analyst with Blaylock & Partners. "If Wal-Mart was hiring from sweatshops, that would be much worse."
"Where this could hurt the company is in its reputation of not being a great place to work. If left unchecked, it could have an impact on Wal-Mart's image," said John Allen, senior partner with corporate brand consultant Lippincott & Margulies.
The largest numbers of arrests occurred in Pennsylvania and Texas, officials said.
Other states where arrests occurred were Alabama, Arkansas, Arizona, Connecticut, Delaware, Kentucky, Massachusetts, Maryland, Michigan, North Carolina, New Hampshire, New Jersey, New York, Ohio, Oklahoma, South Carolina, Tennessee, Virginia and West Virginia.
Wal-Mart (WMT: up $0.46 to $58.70, Research, Estimates) stock edged higher in late trading on the New York Stock Exchange.
-- from staff and wire reports