Arizona Law: Why States Shouldn't Control Immigration Whatever the Supreme Court's decision on Arizona's controversial law, it should be a wake-up call about why American immigration policy must be established on a national - not state - level Jonathan Gibby / Getty Images Protesters opposed to Arizona's immigration law SB 1070 march through downtown Phoenix on April 25, 2012 Cohen is the author of Nothing to Fear: FDR's Inner Circle and the Hundred Days that Created Modern America If the Supreme Court upholds Arizona's law getting tough on undocumented immigrants, as many observers expect, it would not just be approving one state's crackdown. It would be giving a green light to other states to pass similar laws - and it is likely that at least some would. That would be unfortunate: what Americans need is not state-by-state policies but a comprehensive federal solution to the immigration problem. The court heard arguments last month in a challenge to the Arizona law. The goal of SB 1070 is "attrition by enforcement" - prodding illegal immigrants to leave the country by aiming a series of harsh criminal laws at them. Arizona made it a crime to be in the state without proper immigration papers. And it required police to check the immigration status of anyone they arrest if they have "reasonable suspicion" the person is not there legally. There is a bitter debate over SB 1070. Supporters argue it is necessary because the federal government is not serious about enforcing immigration laws. They say Arizona has been flooded with illegal immigrants who have hiked the crime rate, overwhelmed the social-services system and driven down wages. Critics respond that the law is mean-spirited and that it will hurt innocent people, including children. They also say it will be used to harass Hispanics, including American citizens. PHOTOS: Immigration Detention in Arizona The legal challenge to the Arizona law has focused not on these broad objections but a more technical legal one: Does the law conflict with federal immigration law? The Obama Administration, which brought the challenge, argues that immigration is a federal matter and that the laws Congress has passed trump any state laws in the area, based on a legal principle known as pre-emption. Lower courts have blocked parts of the law, but it could be a different story in the Supreme Court. Based on what the Justices said at argument, it seems they are prepared to uphold the whole law. If they do, it could open the floodgates. Five states - Alabama, Georgia, South Carolina, Indiana and Utah - have already passed laws like Arizona's, which are on hold. Those laws could take effect, and other states might enact laws of their own. William Gheen, president of the Americans for Legal Immigration Political Action Committee, told the Associated Press that he believes his group and its allies could pass Arizona-style laws in "most states." That may be an overstatement, but it is likely that at least some new states would jump in. Advocates for illegal immigrants are, naturally, worried - they fear harsh new laws and crackdowns in state after state. But even people who take a harder line on immigration should not be particularly pleased if this is how things go. There is a good reason that we look to the federal government - and not the states - to take the lead on immigration law. Only Congress can address the issue in all its complexity, taking on the many concerns on all sides. MORE: Do Elected Officials Have to Speak English? The Comprehensive Immigration Reform Act of 2007, which never passed, showed what Congress could do. That bill would have created a clear path to citizenship for the estimated 11 million illegal immigrants currently in the U.S. It also had real get-tough provisions, including increased enforcement along the U.S.-Mexico border and a national database for employers to check the immigration status of job applicants. States cannot do anything this ambitious. They may be able to hound individual immigrants into leaving the country or drive the ones who remain to live their lives in the shadows. But states cannot give people a path to citizenship or create a national database. They cannot fix a national system that almost everyone agrees is badly broken. The main reason that Arizona, Alabama and other states have begun acting aggressively on immigration is that Washington has failed for years to address the problem. Even if the Supreme Court says that states have the legal right to enact immigration laws like Arizona's, that does not mean that it makes any sense for the nation's immigration policy to be established at the state level. Whatever the outcome of the challenge to Arizona's law, it should be a wake-up call to Congress that the American people are tired of waiting for immigration reform. Cohen, the author of Nothing to Fear, teaches at Yale Law School.