South Carolina: S.C. Code Ann. § 12-36-2120
S.C. Code Ann. § 12-36-2120. Exemptions from sales tax.
Exempted from the taxes imposed by this chapter are the gross proceeds of sales, or sales price of:
(1) tangible personal property or receipts of any business which the State is prohibited from taxing by the Constitution or laws of the United States of America or by the Constitution or laws of this State.