From this:

States have the authority to enforce immigration laws and protect their borders, Michigan Attorney General Mike Cox said Wednesday in a legal brief on behalf of nine states supporting Arizona's immigration law.

Cox, one of five Republicans running for Michigan governor, said Michigan is the lead state backing Arizona in federal court and is joined by Alabama, Florida, Nebraska, Pennsylvania, South Carolina, South Dakota, Texas and Virginia, as well as the Northern Mariana Islands...

"By lawsuit, rather than by legislation, the federal government seeks to negate this preexisting power of the states to verify a person's immigration status and similarly seeks to reject the assistance that the states can lawfully provide to the Federal government," the brief states.