As a child, Traci Hong came from South Korea to the United States as a legal immigrant. Fifteen years ago, she became a U.S. citizen. Yet in March, when Hong, now 37, applied for a congressional staff job, an employee screening system that is the linchpin of the Senate’s immigration legislation told a different story: It flagged her as being here illegally.

Hong spent eight days navigating the bureaucracy to correct a database error and convince officials that she was entitled to work here — and she’s an immigration lawyer, a graduate of the University of Texas at Austin and its law school.

The screening system, called Basic Pilot, is run by the Department of Homeland Security. So far, it’s being used by only about 16,700 employers — 2,100 or so in California — out of 7 million nationwide.

But it would dramatically expand into a national electronic employment verification system under the Senate proposal; within 18 months, it could be used to check every new hire in the country. As the legislation is written, all 150 million workers in the U.S. would have to submit to the checks within three years.

Supporters call Basic Pilot an efficient blueprint to increase enforcement of laws that bar the hiring of illegal immigrants. It is a central component of what has been dubbed the "grand bargain" between Democrats and Republicans on immigration; in fact, the bill’s proposed guest worker program couldn’t begin until the verification system was capable of screening every new hire in the country.

But opponents — who include conservatives, small businesses, human resource managers and civil liberties groups — are dubious. They say the current program infringes on privacy, doesn’t stop identity fraud and will become more expensive and cumbersome as it expands, bogged down by technical problems and a database with inaccurate information.

Businesses check eligibility by submitting information from an I-9 form, required of all new hires, which includes Social Security and other documentation showing an employee’s right to live and work in the U.S.

If the information is valid, the system sends the business a confirmation. If not, a "tentative nonconfirmation" is returned, and the business asks the employee to provide additional proof of identity or citizenship. Files are even checked by hand before the government finally identifies an employee as illegal.

Although the Internet-based process usually takes seconds, any glitch can take days to resolve. About 200 businesses join the program each week; so far this year, Basic Pilot has processed 1.7 million inquiries — the same as in all of 2006.

Even as more businesses join the program, the system’s error rate of 5% is falling. But a Social Security Administration report last year estimated that 17.8 million Social Security records, or 4.1%, contained discrepancies that could tie up the system.

Traci Hong, for example, was stopped because her records, like those of 7% of naturalized foreigners, failed to indicate that she had been granted U.S. citizenship. A change in immigration status, marriage or divorce needs to be reported to Social Security, said Moran of the National Immigration Law Center.

Basic Pilot has become popular as workplace enforcement becomes a grass-roots issue.

This year, lawmakers in 41 states are considering legislation to strengthen workplace enforcement of immigration laws, according to the National Conference of State Legislatures. The Tennessee Senate approved a bill this spring mandating the use of Basic Pilot by all employers in the state; Rhode Island lawmakers are considering a similar measure.

Proponents say it is the most affordable way to crack down on illegal immigrants.