The Post has a piece this morning about the non-enforcement of laws against hiring undocumented workers. The article includes several statements, including one from Homeland Security Secretary Michael Chertoff, to the effect that native born citizens will not do the jobs that are filled by undocumented workers. Believers in markets would say that if wages rose, then plenty of native-born citizens would be willing to fill the jobs.
Interestingly, meat processing is one of the industries discussed in the article. Thirty years ago, this was an industry with relatively high-paying (albeit extremely unpleasant) jobs. It was also relatively highly unionized. Plenty of native born citizens wanted these jobs.
The Times had a much more insightful piece on the same topic. It reports on the growing use of undocumented workers as custodians and how this has been associated with a decline of wages in the occupation.