|SB1070 protest poster, courtesy NuevaRaza|
In Arizona et al. v. United States, the Opinion of the Court, by Justice Kennedy, held that Congress gave the Federal Government's power over regulating immigration. This authorization has preempted state law, and therefore does not leave room for states to legislate on this matter. Several provisions of SB1070, therefore, violate the Supremacy Clause.
The first problematic section, Section 3, set up a state registration program, violating the intent for the Federal plan to be a "single integrated and all embracing system."
Another problematic section, 5(c), which made it a crime for an undocumented alien to be employed by the State of Arizona, violates the federal scheme, which criminalized employees for employing "illegal aliens", but not the aliens themselves.
Section 6, which is most of concern to criminal justice enthusiasts, allowed local police officers to make warrantless arrests of certain aliens suspected of being removable. The Supreme Court unequivocally states that it is not a crime, generally, for a removable alien to remain in the United States, and it is only at specific stages of the removal process that there is authorization for arrest, such as when the alien is "likely to escape before a warrant can be obtained." The state system is not the one created by congress, and thus violates the Supremacy Clause.
It is important to state, however, that section 2(b) has remained intact. It allows for mandatory checks and has some limitations (such as the presentation of a valid AZ driver's license and the prohibition on racial profiling.) According to the Supreme Court, enjoining that section is premature, as it is not yet clear whether local police will enforce it in a discriminatory fashion, or detain people for longer than required to check their immigration status.