From an LAT guest editorial "Rise of the Off-the-Books Workforce: Native-born workers are being displaced by new immigrants":

If you scrutinize the U.S. labor market numbers from the last two years of economic recovery, you're left with what seems to be a paradox. Since the recession's low point, in November 2001, the number of employed people 16 and older has risen, but the number of jobs on the formal payrolls of employers remains below recessionary levels...

...Employment gains are among the self-employed and contract workers, or in the informal "gray" and "black" labor markets. People are doing temporary day work or contracting that's kept off the books. These don't tend to be highly paid jobs or jobs with benefits like health insurance, and they are often performed by immigrants, especially undocumented immigrants...

...the employment numbers demonstrate that the president's proposal cannot be defended on economic grounds.

The numbers suggest that native-born workers - particularly teenagers and young adults without college degrees - are being displaced by new immigrants. Indeed, last year the employment rate for teens reached a record low, down 9 percentage points since 2000. These are the very people who might benefit from the unskilled jobs now going to foreign workers. Over the last two decades, two-thirds of all the new jobs created in the U.S. have been ones that required at least some college. The earnings gap between college graduates and high school graduates has widened, as has the gap between high school graduates and dropouts. Large increases in unskilled immigrant workers have helped fuel real-wage declines at the bottom of the labor market and increased earnings inequality. Any policy that supports this trend cannot be justified.

The proposed guest-worker program will expand supply in an already oversupplied labor market, foster the further development of a substratum outside of existing laws and customs that regulate employment, and further diminish the chances of teens and other young adults, especially from low-income and minority communities, to get valuable work experience.

Immigration can play an important role in the long-term economic prosperity of the nation. But a guest-worker program that expands immigration in the middle of a jobless recovery is not the answer. Rather than rush into a faulty program to encourage foreign workers, we need to engage as a nation in a sustained and comprehensive national debate on how to best align immigration policy with our nation's short- and long-terms skill requirements - and with the goal of achieving greater economic justice for native-born workers.