All immigrants are required to submit proof that they are in the country legally when they are stopped in Arizona. This is true everywhere else as well. When you get pulled over by the cops you have to show them who you are. If you are illegal you get arrested the same as anywhere else.
The Arizona illegal immigration law may be stricter than any of the other states but that does not make it unconstitutional. People tend to forget that illegal immigrants are criminals. If aliens want to come into this country they should do it legally. I commend Arizona for taking the problem so seriously.