Edward A. Zelinsky (Cardozo) has posted The Constitutionality (and Futility) of Colorado’s Amazon Law, 56 State Tax Notes ___ (2010), on SSRN. Here is the abstract:

Colorado’s law Amazon is constitutional, but will not raise significant revenue for Colorado’s treasury. Most prominently, Colorado’s Amazon law does not reach Amazon or Amazon’s sales to its Colorado customers. Only Congress can effectively address the problem at which the various Amazon laws are aimed by authorizing the states to impose sales and use tax enforcement duties on internet (and mail order) sellers lacking physical presence in the taxing states. In light of the demonstrated ability of “big box” retailers to collect states taxes on their internet sales, Congress should now enact legislation to equalize the sales tax treatment of all online sales.