For a significant period of time, since 1873 in fact, the Supreme Court has held that the taxing power of the states is limited by the dormant commerce clause. State taxes on interstate activity must be “fairly apportioned,” meaning that if more than one state may legitimately tax the same income, each state may only tax its fair share. This flows from the Commerce Clause’s negative converse, i.e. its restriction prohibiting states from enacting legislation that overly burdens or discriminates against interstate commerce. In many cases dealing with the taxation of multi-state businesses, courts have enforced the requirement that state taxes be fairly apportioned.