In my paper, "Electronic Employment Eligibility Verification: Franz Kafka's Solution to Illegal Immigration," I analyzed a number of different factors that would frustrate a national employment eligibility verification system. Most of them had to do with responses that undermine the functioning of the verification system itself. But I also talked about avoidance. Under a national electronic employment eligibility system, I wrote, "[w]ork 'under the table' would increase, and, along with it, other forms of illegality."
Strong validation of that notion came from an interesting source last week: the Congressional Budget Office. CBO and the Joint Committee on Taxation estimate that the SAVE Act (the "Secure America Through Verification and Enforcement Act"), a bill to take E-Verify national, would result in lost federal revenue of $17 billion over 10 years. That is because more undocumented workers would be paid outside the tax system. That's a lot of work under the table.
Those who have fixated on immigration law enforcement often cite the rule of law, which is certainly an important thing. But the rule of law thrives when the law is at peace with the people, not when it's a cudgel. As I also wrote:
Proponents of internal enforcement and electronic employment verification surely stand on a sound principle—the rule-of-law ideal that people should enter the country legally. But current immigration law is a greater threat to the rule of law than any of the people crossing the border to come here and work. Our immigration policies have fostered the illegality so common in the employment area.