Soon after immigration agents arrested 145 workers at a Hyrum meat packing plant back in December 2006, it became publicly known that the parent company, Swift & Co. was checking its workers using a federal Internet-based verification system.

The problem: Workers weren't just using phony Social Security numbers, they were using entire stolen identities. So, even though the company checked that the name, Social Security number and birth date matched, it didn't tell the company the identity didn't match the worker.

Utah's senators today are scheduled consider a key question: should the system, now called E-Verify, be required for public employers and those they contract with. Those proposals are included in SB81, a comprehensive bill aimed at preventing illegal immigrants from getting jobs or public benefits. SB81 also creates a Class A misdemeanor for those who harbor or transport illegal immigrants.

Supporters of that system say it does weed out most phony work documents. And they point out the federal system has been vamped up since 2006 and is now more accurate. There's a proposal for $100 million more in improvements to the system, which now has a growing photo database with 15 million images so far, according to U.S. Citizenship and Immigration Services.

But opponents point to Swift & Co.'s experience as evidence the system isn't perfect and say that workers who are incorrectly marked as no-matches have the burden of proving their work eligibility.

Derek Dastrup, account manager for Westaff, a Taylorsville staffing agency, verifies several new hires each month using E-Verify. It's a system Dastrup describes as simple to use and nearly always accurate.

"The fact of the matter is it's a very good tool to use," Dastrup says. "It basically gets rid of any risk for Westaff and our clients ... of employment being problematic."

However, critics, including Tom Bingham, president and chief executive officer of the Utah Manufacturers Association says Swift is a perfect example of why the program shouldn't be required.

"The problem we have, is the E-Verify system doesn't do what it purports to do," Bingham said.

And while Swift hasn't been charged, avoiding criminal prosecution isn't enough to shield employers, Bingham says. The company's Hyrum location lost 145 workers in one day — and a total 1,300 at locations across the country.

"They didn't get charged yet," Bingham said of Swift. "But they were nearly put out of business in Hyrum. All the time, they were assuming they had hired and trained legal employees."

Bingham is among several business leaders who have announced their opposition of SB81, and the House bills. They instead favor another Senate measure, SB97, which would create a task force to study the issue.

The employers are also concerned about other provisions in SB81, including one to create a private cause of action for legal workers to sue if they're fired by employers who also employ undocumented immigrants.

SB81 is modeled after a new Oklahoma law, which is considered one of the nation's toughest crackdowns on illegal immigration. That law has prompted a federal lawsuit filed by a coalition of business leaders including the Oklahoma Chamber of Commerce.

Anecdotal evidence points to Oklahoma law has caused an outflux of many of that state's estimated 100,000 undocumented immigrants. In that state, construction companies are have problems completing jobs and businesses that cater to Hispanic clientele are suffering, The Chicago Tribune has reported.

E-Verify is used by more than 52,000 employers nationwide. There were nearly 3.3 million employees checked by the system in fiscal year 2007 and more than 1.7 million checked so far in this fiscal year, according to CIS.

Some 93 percent of the people who are checked by the system are immediately given an OK to work, according to CIS. Of the remaining, 7 percent, roughly 1 percent take steps to rectify the situation through either CIS or the Social Security Administration.

The implication is that the remaining six percent take themselves out of the process, "they know they're not eligible to work ... they self disqualify," said Maria Elena Garcia-Upson, an agency spokeswoman.

A report done for CIS by the Maryland-based Westat last points specifically to the program's ability to accurately verify the work eligibility of naturalized citizens.

"The accuracy of the USCIS database used for verification has improved substantially since the start of the Basic Pilot program," the report states. "However, further improvements are needed ... "

When it comes to errors, Dastrup says, there haven't been many issues, though a few people have had to correct their information.

"Very, very rarely to do we run into an issue that needs to be followed up on," he said.

Only 0.1 percent of U.S.-born employees were considered no-match, according to the report. However, that rate was 3 percent for foreign born employees. Naturalized U.S. citizens were more likely than work-eligible non-citizens to be considered mismatches, although Garcia-Upson said the agency is trying to address that problem.

That discrepancy is troubling to immigration attorney Roger Tsai, especially given that under E-Verify, employees have only 10 days to clear up a no-match with the Social Security Administration or with CIS.

"There is no hotline for them to call," he said. "It's still kind of questionable what people are supposed to do."

And Tsai said, employers who hire large numbers of immigrant workers could also face a challenge given the error rate for foreign born workers is 30 times that of U.S. natives.

"It puts employers at the mercy of these federal records that may or may not be inaccurate," Tsai said. "E-Verify is extremely strict."

But advocates for the program, including Ron Mortensen, co-founder of the Utah Coalition on Illegal Immigration, says that workers whose information doesn't match up — such as newly wed women who forgot to report a name change — eventually need to clear up those discrepancy anyway.

And Mortensen says that E-Verify would weed out most unauthorized workers who use random Social Security number and random name. It will also, Mortensen says, catch those who steal a child's identity, because employers would notice a 50 year old using a 4-year-old's birthday, Mortensen says, adding, "Wouldn't it be great to say, 'hey, we're protecting your kid's identity from identity theft."'