Enlarge By Joe Raedle, Getty Images A road construction crew works on a widening project in February in Florida City, Fla. The stimulus law calls for infrastructure projects to help spark the economy. LOS ANGELES  Tens of thousands of jobs created by the economic stimulus law could end up filled by illegal immigrants, particularly in big states such as California where undocumented workers are heavily represented in construction, experts on both sides of the issue say. Studies by two conservative think tanks estimate immigrants in the United States illegally could take 300,000 construction jobs, or 15% of the 2 million jobs that new taxpayer-financed projects are predicted to create. They fault Congress for failing to require that employers certify legal immigration status of workers before hiring by using a Department of Homeland Security program called E-Verify. The program allows employers to check the validity of Social Security numbers provided by new hires. It is available to employers on a voluntary basis. JOBS FORECAST: Where the jobs are, state by state STOCKS RECOVERY: Could take years "They could have deterred this, but they chose not to," said Steven Camarota, director of research for the Center for Immigration Studies. He said a federal requirement that employers use E-Verify would have reduced, if not eliminated, the hiring of immigrants in this country illegally. An advocacy group for immigrants, illegal and legal, did not disagree with the 300,000 estimate. Camarota says the estimate is based on data from the U.S. Census Bureau's Current Population Survey and other independent findings that 15% of all construction workers in the USA are either illegal immigrants or lack the status of legal immigrant authorized to work. But Jorge-Mario Cabrera, director of education for the Coalition for Humane Immigrant Rights of Los Angeles, said it is impossible to predict with certainty because it is unknown how many jobless immigrant construction workers may leave the U.S., frustrated by the economic recession, before the new spending produces jobs. He questioned the Center for Immigration Studies' motives. "Those are fear tactics. … 'The immigrants are here to take your job,' " Cabrera said. "I think that we really should be focusing on economic progress for all." The center is a Washington policy organization that, its website says, "seeks fewer immigrants but a warmer welcome for those admitted." Cabrera says his group believes unauthorized immigrants working in this country contribute to the economy. A similar hiring estimate was produced in a report in February by the Heritage Foundation, a conservative think tank. Senior research fellow Robert Rector wrote, "Without specific mechanisms to ensure that workers are U.S. citizens or legal immigrants authorized to work, it is likely that 15% of these workers, or 300,000, would be illegal immigrants." The version of the stimulus bill passed by the House of Representatives included a provision requiring employers to check immigration status with the E-Verify system before hiring. The Senate did not include such a provision, and it was not in the version sent to President Obama. The Obama administration has delayed until at least May 21 a Bush administration executive order requiring federal contractors to use the E-Verify system in hiring. It had been scheduled to take effect in January. The U.S. Chamber of Commerce filed suit seeking to block the requirement, joined by the Associated Builders and Contractors and other business organizations. The business groups and immigrant advocacy groups argue that the E-Verify database is riddled with errors that could result in millions of workers being wrongly identified as not authorized for work. They say requiring its use before hiring would impose a cost burden on employers and open them to lawsuits. Camarota said illegal immigrants working in construction are concentrated in California, Arizona and Texas along the border with Mexico, as well as Florida, Illinois, New York, New Jersey, North Carolina and Georgia. Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more