The U.S. Supreme Court case over Arizona’s latest anti-immigration law, scheduled for a hearing next week, hinges largely on the question of where states’ power over immigration ends and federal power begins. But in a sign of how contentious the case is, many states are supporting the federal government instead of Arizona.

Eleven states, all represented by Democratic attorneys general, warned the justices that Arizona’s law reached too far and undermined the immigration policy of the United States. However much Arizona may disagree with federal policies on immigration enforcement, they wrote in a friend-of-the-court brief, “it cannot operate its own unilateral removal policy outside of any federal oversight.”

The case, Arizona v. United States, centers on a law passed by Arizona lawmakers two years ago, known as Senate Bill 1070. The measure requires local police to check the immigration status of a criminal suspect if they have “reasonable suspicion” that the suspect is in the country illegally. The Obama administration sued to block the law, and most of the law is on hold during the appeal.

Sixteen states support Arizona’s position. Of those, all but West Virginia are represented by Republican attorneys general. They say that Arizona’s law does not interfere with federal immigration policies, and in fact, the measure helps the federal government enforce its own immigration laws.