The National Research Council has estimated that the net fiscal cost of immigration ranges from $11 billion to $22 billion per year, with most government expenditures on immigrants coming from state and local coffers, while most taxes paid by immigrants go to the federal treasury. The net deficit is caused by a low level of tax payments by immigrants, because they are disproportionately low-skilled and thus earn low wages, and a higher rate of consumption of government services, both because of their relative poverty and their higher fertility.
The letter does not deal with taxes only with average income.