The U.S. Supreme Court has saved one of its highest-profile cases for the last scheduled public hearing of the 2011-2012 term. It was scheduled to hear oral arguments today in Arizona v. United States, a dispute over the controversial state immigration law Arizona enacted in 2010.

Lower courts ordered Arizona not to enforce four key provisions of the law, ruling that they essentially set up a separate state-level system of immigration law and enforcement. That conflicts with the national system devised by the executive branch with the authority of Congress and the Constitution. In such situations, federal law preempts and invalidates state law.

The Supreme Court should affirm the findings of the lower courts. Arizona's Senate Bill 1070 became controversial for the likelihood of encouraging racial and ethnic profiling and harassing people solely on the basis of their appearance, their accents, their apparent economic status or various combinations of all three. But possible breaches of civil rights and due process are not before the Supreme Court.

Instead, the Justice Department has challenged four provisions that most clearly illustrate the conflict between Arizona's alternative immigration scheme and the federal system.

One provision, for example, requires state and local law enforcement officers to detain anyone they suspect of having entered the country illegally and keep them in custody until their status is determined to be valid. A second authorizes law enforcement officers to conduct warrantless searches based on a suspicion that someone may have committed a crime that would be grounds for deportation.

The third provision being challenged makes it a state crime for a person to be without proof of citizenship, government-issued identification or documents affirming authorized immigrant status. The fourth makes it a state crime for immigrants to apply for work, accept work or even make themselves available for work if their presence in the United States is unauthorized.

On one hand, Arizona argues in its brief to the Supreme Court that its law simply establishes "parallel" state efforts to enforce federal law and enhances cooperation and communication between state and federal authorities. Yet in other sections of the brief, Arizona invokes unrestricted state police power to maintain law and order.

Arizona can't have it both ways. Contrary to SB 1070, federal law does not criminalize work. An immigrant who lacks official authorization to be in the United States is not guilty of a federal crime, but he would be guilty of a state criminal offense under SB 1070.

More than anything else, the federal system allows for discretion in adopting strategies and setting enforcement priorities in response to changing circumstances. The Arizona system rejects that federal approach entirely and tried to eliminate discretion.

America's immigration system has many serious problems and long has needed new federal legislation to address them. But the system hardly is non-functional. A Congressional Research Service report released in January offers a detailed overview.

The ugly truth is that the Republican majority of elected Arizona state officials in 2010 decided they didn't like the federal immigration system and decided to create their own. They have every right to not like the federal system and to work to change it; they have no right to concoct one of their own to supplant it.

The Supreme Court should reject Arizona's disingenuous arguments.

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