Connecticut: Conn. Gen. Stat. § 12-412

Conn. Gen. Stat. § 12-412. Exemptions.
Taxes imposed by this chapter [Sales and Use Taxes] shall not apply to the gross receipts from the sale of and the storage, use or other consumption in this state with respect to the following items:
(2) Federal exemptions. Sales of tangible personal property or services which this state is prohibited from taxing under the Constitution or laws of the United States.