Congress this week approved the extension of the federal E-Verify program for three years, through September 30, 2015. Originally established in the late 1990s and launched nationwide in 2003, E-Verify is a free Internet-based service through which employers can verify their employees’ legal right to work in this country. The program compares each employee’s I9 Employment Eligibility Form with U.S. government records in order to determine which individuals are working here illegally. E-Verify was set to expire at the end of this month

Currently, E-Verify is offered to employers on a voluntary basis nationally, but 19 states have passed legislation mandating that at least some employers there register for and use the program. In Arizona, the government mandates that all employers verify their employees’ legal right to work in the state through E-Verify. For proponents of the program, Arizona became a national model for the extension of the E-Verify mandate earlier this year when presidential candidate Mitt Romney singled out the law as an example of smart immigration enforcement. For Romney, who favors a federal law requiring all employers to use E-Verify, the program is a key element in his chosen immigration enforcement strategy of “self-deportation.” As undocumented immigrants find themselves unable to find work in the United States, Romney posits, they will return to their countries of origin.

Those in favor of E-Verify argue that it benefits states that mandate its use in a number of ways. It is as yet unclear precisely how effective E-Verify is in actually stopping undocumented individuals from being hired in states where employers use it. Some reports state that more than half of undocumented immigrants vetted by the program are ultimately cleared to work.