central government upon a single item of export would apply very unevenly amongst all the states and favor states which did not export that good. In 1996, the Supreme Court held this provision prohibits Congress to tax any goods in export transit, and further forbids taxes on any services related to such export transit. Shortly after, the Supreme Court reaffirmed this provision in United States v. United States Shoe Corp. in 1998. As part of the Water Resources Development Act of 1986, a harbor maintenance tax () was imposed at the ad valorem (percentile) rate of 0.125% the value of the cargo instead of at a rate dependent entirely upon the cost of the service provided by the port. The Court unanimously affirmed the ruling of the lower Federal Circuit Court that a "user fee" imposed in such a manner is, in fact, a tax on exports and unconstitutional. However, Congress may tax goods not in transit even though they are intended for export so long as the tax is not imposed solely for the reason that the good will be exported. For example, a tax imposed on all medical supplies would be constitutional even though there is a likelihood a portion of those supplies will be exported. Restrictions on spending The constraints placed upon the Taxing and Spending Clause and the subsequent powers derived therefrom do not stop at the Taxing Power. Disguised regulations While such holdings are rare and unlikely under contemporary jurisprudence, the Supreme Court has shown in the past its possible willingness to intervene on Congressional spending where its effects amount to a disguised regulation on private activity. The case illustrative of this is United States v. Butler. In this case, the Court held that Congress had imposed a coercive federal regulatory scheme on farm production under the Agricultural Adjustment Act of 1933 (AAA). By entering into contracts with farmers who reduced their output of selected crops, Congress had placed non-participating farmers at a distinct disadvantage to farmers who cooperated. As such, the program was not truly voluntary as it left the farmers no real choice; the options for the farmers were either cooperation or financial ruin. Under those circumstances, the regulatory scheme essentially required submission of farmers to a regulatory scheme Congress had no power to impose on its own. The holding of the Butler case stemmed from the legal theory of that era, which