Over the same period, more than 40% of approved H-1B workers were approved to fill occupations in systems analysis and programming, the GAO reported.

Among the findings is that H-1B workers are "often not paid wages associated with the highest skills in their fields." The report found that 54% of the workers from June 2009 to July 2010 "were categorized as entry-level positions and were paid at the lowest pay grades allowed under prevailing wage levels."

In a comparison of median annual salaries reveals that for systems analysts, programmers, and other computer-related workers, the GAO said that H-1B workers tended to earn less than U.S. workers, but some of this salary gap appears explained by differences in ages and experience, it noted.

The widest wage differential is for H-1B workers aged 40 to 50. They had median reported earnings that were significantly lower than the median earnings of U.S. workers in these IT occupations, the GAO reported.

But the GAO wasn't able to determine, definitively, the impact of H-1B visa use of the wages of other workers.