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.