challenging a state law requiring immigrants to carry their registration papers at all times, and allowing the police to question residency status. the justice department says that the immigration is a federal matter and suing to stop the law from taking effect at the end of this month. we have comprehensive coverage this hour, and we will hear from some key players, but let's begin with cnn's lisa sylvester who has the latest. lisa? >> wolf, the justice department is basing the argument on preemption in that the states can not pass law that preempts federal law. in this case, the justice department is asking the state of arizona for an injunction to keep the law from taking effect at the end of this month, and to take a step further to declare the law null and void. >> reporter: this new law would make illegal immigration a state crime, and it would make them