For those of you, who want to argue the constitutionality of the Arizona immigration bill. Well here you go. Try to argue against Supreme Court precedent.
The courts have long recognized that by Article I, Sec. 8 of the U.S. Constitution (the Commerce Clause), Congress has “plenary power” over all aspects of immigration law, including “the right to provide a system of registration and identification” for aliens, because “the entire control of international relations” is invested in the national government. Courts have repeatedly held that no governmental authority may establish any policy that relates to immigration other than Congress and authorized federal agencies, and that the “(p)ower to regulate immigration is unquestionably exclusively a federal power.”
Thus, a local governmental public policy to accept an official foreign national identification document issued to aliens present in the United States in violation of Federal law improperly annexes powers to any public entity that are rightfully those of Congress and the policy is therefore unconstitutional.
In a Supreme Court decision striking down a Pennsylvania alien registration statute, it was held that the “Federal Government…is entrusted with full and exclusive responsibility for the conduct of affairs with foreign sovereignties [, and that o]ur system of government is such that the interest of the cities, counties and states, no less than the interest of the people of the whole nation, imperatively requires that federal power in the field affecting foreign relations be left entirely free from local interference.”
The Court ruled that “where the federal government, in the exercise of its superior authority in this field, has enacted a complete scheme of regulation … states cannot, inconsistently with the purpose of Congress, conflict or interfere with, curtail or complement, the federal law, or enforce additional or auxiliary regulations.” Therefore, no public entity, specifically Boulder City and County, as defined above, may make any rule, regulation or policy that speaks to the presence in the community of foreign nationals, and, thus, a “matricula consular policy” is preempted on constitutional grounds. A “matricula consular” policy adopted by local governmental authorities has also been determined unconstitutional specifically in relation to public benefits because it violates “the exclusive federal power over the entrance and residence of aliens.” (via CAIR)
Here are the actually Supreme Court cases.
 De Canas v. Bica, 424 U.S. 351 (1976)
 Hines v. Davidowitz, 312 U.S., at 66 -67
 Graham v. Department of Pub. Welfare, 403 U.S. 365 (1971) (USSC+)