Wyoming: Wyo. Stat. § 39-15-105; WCWR 011-000-002

Wyo. Stat. § 39-15-105. Exemptions
(a) The following sales or leases are exempt from the excise tax imposed by this article:
(i) For the purpose of exempting sales of services and tangible personal property which are protected by the United States constitution and the Wyoming constitution, the following are exempt.
(A) Sales which the state of Wyoming is prohibited from taxing under the laws or constitutions of the United States or Wyoming.

WCWR 011-000-002. SALES AND USE TAX.

Section 7. Non-Taxable and Exempt Sales Transactions.

(b) Certificates of Exemption.

  (i) Vendors shall obtain completed exemption certificates for all sales transactions, other than those qualifying under section 6 of these rules, where sales tax is not collected from the purchaser at the time of sale. Purchasers shall file a single exemption certificate with each selling vendor for exempt purchases made. The certificates shall be in a format as prescribed by the Streamlined Sales and Use Tax Agreement and shall be retained in the selling vendor's records. The seller shall obtain identifying information of the purchaser and the reason for claiming a tax exemption at the time of the purchase. A purchaser is not required to provide a signature to claim an exemption from tax unless the paper exemption certificate is used. The seller shall use the standard format for claiming an exemption electronically when that format is adopted by the Governing Board of the Streamlined Sales Tax Project.

  (ii) Vendors shall be relieved of the tax otherwise due if the seller obtains a fully completed exemption certificate or captures the relevant data elements listed in subsection (i) above within ninety (90) days of the date of the sale.