14th amendment
Wouldn't such a law violate the 14th amendment (the 'equal protection' clause)? In other words, the U.S. constitution states that citizens and non-citizens should be treated in the same way, with some limited exceptions.
"Are Foreign Nationals Entitled to the Same Constitutional Rights As Citizens?
David Cole, Georgetown University Law Center"
http://scholarship.law.georgetown.edu/cgi/viewcontent.cgi?article=1302&context=facpub
Of course, having the resources to be able to demonstrate standing and take this all the way to the Supreme Court of the US might be a little tricky.
Biting the hand that feeds IT
