Even wages earned illegally in the U.S. are taxed. Individual Taxpayer Identification Numbers (ITINs) are available to people without Social Security numbers who cannot legally work in the U.S. so they can file tax returns.

An April study by the Institute for Taxation and Economic Policy found that undocumented immigrants paid $11.2 billion in taxes in 2010. It estimated that nearly half of all illegal immigrants pay income taxes.

"Undocumented immigrants are undoubtedly positive for the fiscal health of this country," says Leticia Miranda, associate director of the Economic Policy Project at National Council of La Raza, a group that advocates for Hispanics in the U.S.  She says that harping on the number of undocumented immigrants glosses over the bottom line that these workers are paying hefty sums into the Social Security trust fund, despite having no claim on the benefits. The Social Security Administration's chief actuary estimated last year that undocumented immigrants had paid $120 billion to $240 billion into the Social Security trust fund as of 2007.

According to the Treasury Department's Inspector General, in 2010, ITIN filers reported $60 billion dollars in wages, which according to an estimate by the National Immigration Law Center means they generated an estimated $9.2 billion in payroll taxes. If the marginalization of illegal immigrants made it impossible for people to make those tax payments, that would be a self-inflicted wound to the budget of this country.

And if these figures represent the less than half of illegal immigrant ITIN-filers, the real figure could be in the order of $20 billion in payroll taxes if the de facto residence of these illegal immigrants was appropriately recognized and they came out of the shadows.