Federal agents raided six Swift & Co. processing plants in six states on Tuesday in search of illegal immigrants who stole the identities of lawful U.S. residents and used their Social Security numbers to get jobs at the beef and pork company.

Agents from the Immigration and Customs Enforcement agency executed search warrants at Swift's processing facilities in Greeley, Colo.; Grand Island, Neb.; Cactus, Texas; Hyrum, Utah; Marshalltown, Iowa; and Worthington, Minn.

ICE officials didn't give the total number of people arrested but said workers were being apprehended on administrative immigration violations and in some cases, existing criminal arrest warrants. The warrants allow federal agents to arrest anyone at the plant who is in the United States illegally.

ICE said criminal charges of aggravated identity theft and other violations were possible. No charges have been filed against the company.

In Greeley, cars lined the street leading to the plant as family members stood outside. One person held a sign that said, "Presents! No tears at Christmas!"

A company statement obtained by FOXNews.com said all the facilities raided except the one in Hyrum are unionized. No civil or criminal charges have yet been filed against Swift or any current employees.

The company said every employee hired since 1997 has completed the proper forms and received proper work authorization from the government.

"Swift has never condoned the employment of unauthorized workers, nor have we ever knowingly hired such individuals," said Swift & Company CEO Sam Rovit. "Swift has played by the rules and relied in good faith on a program explicitly held out by the president of the United States as an effective tool to help employers comply with applicable immigration laws."

A federal investigation that began in February of this year uncovered large numbers of illegal immigrants who may have used the Social Security numbers of lawful U.S. citizens or residents to get jobs at Swift.

Hundreds of potential victims have been identified by immigration officials and the Federal Trade Commission.

ICE, the Department of Homeland Security, FTC and other agencies will hold a press conference on the raids in Washington Wednesday.

"We have been investigating a large identity theft scheme that has victimized many U.S. citizens and lawful residents," ICE spokeswoman Barbara Gonzalez said at the plant in Greeley.

ICE chief Julie L. Myers told reporters in Washington that immigration officials were "looking very aggressively" at who may have sold the identities to the workers in several cases. She said ICE had uncovered several different rings that may have provided illegal documents.

Some immigrants targeted had genuine U.S. birth certificates and others had other kinds of false identification, Myers said.

"The significance is that we're serious about work site enforcement and that those who steal identities of U.S. citizens will not escape enforcement," Myers said

Swift said operations at its facilities have been temporarily suspended and expects that ICE will be finished interviewing employees by the end of the day. Once the company gets back up and running, the statement said, "production levels will depend on the number of employees, if any, detained for further interviewing or otherwise unable to return to work."

Swift said it's not sure how the raids will affect its operations but said "any loss of a significant number of employees" at any one facility could slow things down until those workers are replaced.

Rep. Bennie Thompson, D-Miss., who will chair the House Committee on Homeland Security when Democrats take control of Congress in January, issued a statement applauding ICE's actions, which he said "sends a clear message to businesses and employees across the nation that worksite enforcement and hiring only authorized workers is critical to our nation's safety and security.

"It is the duty of employers to ensure that they are following the letter of the law and only employing people who have a legal right to be here. Those who don't will be penalized," Thompson added.

Swift said it believes Tuesday's raids "violate the agreements associated with the company's participation over the past ten years in the federal government's Basic Pilot worker authorization program and raise serious questions as to the government's possible violation of individual workers' civil rights."

Basic Pilot is a voluntary federal program where businesses can check the legal work status of new employees against government databases. In his fiscal 2007 budget request to Congress early this year, President Bush requested $135 million to expand the current program.

Click here for more information on Basic Pilot

Swift said all of its domestic production facilities have agreements with the federal government under Basic Pilot to protect employers participating employers from government-initiated civil and criminal penalties.

"Current law limits an employer's ability to scrutinize the background and identity of new hires, and — as Swift learned first-hand — employers can, in fact, be punished for probing too deeply into applicants' backgrounds," the company said.

That was in reference to the 2000 complaint filed by the Justice Department's Special Counsel for Unfair Immigration-Related Employment Practices that alleged Swift engaged in a "pattern and practice" of document-based discrimination against job applicants. The department sought civil damages of $2.5 million.

The Justice Department said Swift's Worthington, Minn., plant engaged in discrimination and unfair practices when hiring U.S. citizens and lawful immigrant workers who were believed to look or sound "foreign." Justice claimed those individuals were more heavily scrutinized than others during the employment process.

After two years, Swift settled the claim for about $200,000.

"Swift & Company fully supports comprehensive immigration reform to address the significant policy tension that exists between the need for employers to accurately determine workers' eligibility versus the need to address privacy and non-discrimination concerns," the company said Tuesday. "The company remains committed to preventing the employment of unauthorized workers in its workforce."

With operations in Australia as well as the United States, Swift & Company is the country's third fresh meat processor behind Tyson Foods and Cargill Meat Solutions, with sales of $9 billion a year.

Once the meat-processing business of agriculture giant ConAgra, Swift was spun off and is now indirectly owned through various holding companies such as HM Capital Partners (formerly Hicks, Muse, Tate & Furst) and Booth Creek Management.

Founded in 1855, Swift's customers include retail, foodservice and further-processing companies.

FOX News' Catherine Herridge and The Associated Press contributed to this report.