North Carolina: N.C. Gen. Stat. § 105-164.13
N.C. Gen. Stat. § 105-164.13. Retail sales and use tax
The sale at retail and the use, storage, or consumption in this State of the following tangible personal property, digital property, and services are specifically exempted from the tax imposed by this Article:
Exempt Status Group.
(17) Sales which a state would be without power to tax under the limitations of the Constitution or laws of the United States or under the Constitution of this State.