27 CFR §26.193

1. (a)If the chemist of the Treasury of Puerto Rico finds that denatured spirits or products made with denatured spirits are not eligible for tax-free shipment, before the shipment is made, the chemist will immediately notify the shipper that the article is subject to tax, payable in accordance with §§ 26.107 through 26.110.
2. (b)If the chemist of the Treasury of Puerto Rico finds that denatured spirits or products made with denatured spirits are not eligible for tax-free shipment, after the shipment is made, the chemist will immediately notify the shipper that the tax shall be paid immediately in accordance with § 26.113. The chemist will also notify the appropriate TTB officer.