All information from an I-9 is entered into the system, and it generally takes less than a minute to verify the information, Garrido said. If an employee is found to be ineligible for work, he or she can appeal. Otherwise, the employer must immediately terminate the employee.

Employers can also check Social Security numbers by calling the Social Security Administration or Immigration and Customs Enforcement to find out if a Social Security number is valid.

There are fines ranging from $250 to $10,000 for each unauthorized worker and a maximum six-month prison sentence if a violator demonstrates a persistent pattern of hiring unauthorized workers.

One of the challenges of enforcing the employment law has been a proliferation of counterfeit documents, said Virginia Kice, spokeswoman for U.S. Immigration and Customs Enforcement.

"We have to be able to prove the employer knowingly hired someone who is not authorized to work," Kice said.

In Utah, one of the biggest recent cases was a 2003 raid of Champion Safe in Provo. Federal immigration officials arrested 107 employees. An $80,000 fine was levied against the business after the owner admitted to concealing information about two dozen undocumented immigrants working at the company.

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E-mail: dbulkeley@desnews.com