What is the two step process of analizing a question where state regulation affects the free flow of interstate commerce:
First ask: does the question refer to any federal legislation that might supersede the state reguation or preempt the field or or authroizes state regulation where otherwise permissible? If yes then automatically valid or invalid.
If not, then does the state regulation either discriminate against interstate or out of state commerce or place an undue burden on the free flow of interstate commerce? If discriminatory, it will be invalid unless it furthers an important, noneconomic state interest and there are no reasonable nondiscrimionatory alternatives or the state is market participant.
If the regualtion does not discriminate but burdens interstate commerce, it will be invalid if the burden on commerce outwieghs the states interest