R.I. Gen. Laws § 44-18-32: Sales to federal contractors.

The sales tax imposed by this chapter applies to the gross receipts from the sale of any tangible personal property to contractors purchasing property either as the agents of the United States or for their own account and subsequent resale to the United States for use in the performance of contracts with the United States for the construction of improvements on or to real property, except insofar as the imposition of a sales tax would violate the provisions of the Constitution of the United States.