When there is a less restrictive means available to the state, and the state could accomplish its objective as well it should do so (Wisconsin can't ban all out of state milk for health reasons; would be better to just hire health inspectors - Dean Milk Co. v. Madison) state law which says "you can't bring your goods into our state" or "you can't take goods out of our state into your state" States may not protect their environment at the expense of their neighbors, unless there is no less-discriminatory way to achieve the same result (Philadelphia v. New Jersey)