A report from Westat found that the Department of Homeland Security's E-Verify system inaccurately identifies workers unauthorized for employment in the U.S. as authorized 54 percent of the time.
E-Verify is an online system that compares employee status with more than 444 million records in the Social Security Administration database and more than 60 million records in DHS immigration databases.
Only 6.2 percent of all E-Verify queries related to unauthorized workers, however, and the system is matching up legal workers with the proper status with 99 percent accuracy, according to the report.
The Westat report is based on research from two years ago but was just released in late January on the DHS Web site. Its findings were not widely reported until earlier this week.
The system's inaccuracy percentage drew criticism for the program and vows for reform from lawmakers, in particular Sen. Charles Schumer (D-NY), who is writing an immigration bill for his party.
He said the findings of the Westat report prove it is not an "effective remedy" for preventing employers from hiring unauthorized workers, according to published reports.
E-Verify is currently used by more than 180,000 employers at more than 675,000 work sites. It is mainly a voluntary program and applies only to new hires, not existing employees, at an organization.