And yet, a bill introduced in Congress last year that would have heeded the NIH recommendation by limiting visas for biomedical scientists was attacked in a Forbes article that suggested it could delay progress on the search for a cure for cancer by keeping out able researchers.

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Foreign-born scientists and engineers have, of course, contributed significantly to American society as innovators and entrepreneurs—and the nation’s immigration policy certainly needs repair. But many leading STEM-labor-force experts agree that the great majority of stem workers entering the country contribute less to innovative breakthroughs or job growth for Americans than to the bottom lines of the companies and universities that hire them.

Temporary visas allow employers to pay skilled workers below-market wages, and these visas are valid only for specific jobs. Workers are unable to take another job, making them akin to indentured servants. Universities also use temporary visas to recruit international graduate students and postdoctoral scientists, mainly from China, to do the gruntwork for professors’ grants. “When the companies say they can’t hire anyone, they mean that they can’t hire anyone at the wage they want to pay,” said Jennifer Hunt, a Rutgers University labor economist, at last year’s Mortimer Caplin Conference on the World Economy.

Research by Hira, Norman Matloff of the University of California-Davis, Richard Freeman of Harvard, and numerous others has shown how temporary visas have allowed employers to flood STEM labor markets and hold down the cost of tech workers and scientists doing grant-supported university research. Wages in the IT industry rose rapidly throughout the 1990s, but have been essentially flat or declining in the past decade, which coincides with the rising number of guestworkers on temporary visas.

In his new book, Why Good People Can’t Get Jobs, Peter Cappelli, a human-resources specialist at the Wharton School, concludes that companies’ reported hiring difficulties don’t arise from a shortage of qualified workers, but from rigid recruitment practices that use narrow categories and definitions and don’t take advantage of the applicants’ full range of abilities. Companies so routinely evade protections in the visa system designed to prevent displacement of American citizens that immigration lawyers have produced videos about how it is done. For instance, tech companies that import temporary workers, mainly recent graduates from India, commonly discard more expensive, experienced employees in their late 30s or early 40s, often forcing them, as Ron Hira and other labor-force researchers note, to train their replacements as they exit. Age discrimination, Hira says, is “an open secret” in the tech world.

The temporary-visa system also facilitates the offshoring of STEM work, particularly in the IT field, to low-wage countries. Outsourcing companies use the temporary visas to bring workers to the US to learn the jobs that the client company is planning to move to temp workers’ home country. The 10 firms with the largest number of H-1B visas, the most common visa for high-skill workers, are all in the business of shipping work overseas, and former Indian commerce minister Kamil Nath famously labeled the H-1B “the outsourcing visa.”

These practices have helped to reduce incomes and career prospects in STEM fields drastically enough to produce what UC Davis’s Norman Matloff calls “an internal brain drain” of talented Americans to other, more promising career opportunities such as Wall Street, healthcare, or patent law.

The proposal before Congress to automatically grant green cards to all STEM students with graduate degrees—regardless of field, origin, or quality—would exacerbate the problem of already overcrowded markets, according to new research by Hal Salzman of Rutgers University, Daniel Keuhn of American University, and B. Lindsay Lowell of Georgetown University. It also would benefit universities facing tough financial times by dramatically increasing the allure of American graduate schools, and thus the income potential to universities. And, as Republican Senator Chuck Grassley said at a 2011 hearing, it would “further erode the opportunities of American students. Universities would in essence become visa mills.”

Beryl Lieff Benderly is a fellow at the American Association for the Advancement of Science.