<P> Justice Story characterized this requirement in a light more relevant to practicality and fairness: </P> <P> It was to cut off all undue preferences of one state over another in the regulation of subjects affecting their common interests . Unless duties, imposts, and excises were uniform, the grossest and most oppressive inequalities, vitally affecting the pursuits and employments of the people of different states, might exist . </P> <P> In other words, it was another check placed on the legislature in order to keep a larger group of states from "ganging up" to levy taxes benefiting them at the expense of the remaining, smaller group of states . </P> <P> A somewhat notable exception to this limitation has been upheld by the Supreme Court . In United States v. Ptasynski, the Court allowed a tax exemption which was quasi-geographical in nature . In the case, oil produced within a defined geographic region above the Arctic Circle was exempted from a federal excise tax on oil production . The basis for the holding was that Congress had determined the Alaskan oil to be of its own class and exempted it on those grounds, even though the classification of the Alaskan oil was a function of where it was geographically produced . </P>

Congress shall have the power to lay and collect taxes