26 U.S.C. § 4672

(a) Taxable substance For purposes of this subchapter— (1) In general The term “taxable substance” means any substance which, at the time of sale or use by the importer, is listed as a taxable substance by the Secretary for purposes of this subchapter. (2) Determination of substances on list A substance shall be listed under paragraph (1) if— (A) the substance is contained in the list under paragraph (3), or (B) the Secretary determines, in consultation with the Administrator of the Environmental Protection Agency and the Commissioner of U.S. Customs and Border Protection, that taxable chemicals constitute more than 20 percent of the weight (or more than 20 percent of the value) of the materials used to produce such substance (determined on the basis of the predominant method of production). If an importer or exporter of any substance requests that the Secretary determine whether such substance be listed as a taxable substance under paragraph (1) or be removed from such listing, the Secretary shall make such determination within 180 days after the date the request was filed. (3) Initial list of taxable substances Cumene Methylene chloride Styrene Polypropylene Ammonium nitrate Propylene glycol Nickel oxide Formaldehyde Isopropyl alcohol Acetone Ethylene glycol Acrylonitrile Vinyl chloride Methanol Polyethylene resins, total Propylene oxide Polybutadiene Polypropylene resins Styrene-butadiene, latex Ethylene oxide Styrene-butadiene, snpf Ethylene dichloride Synthetic rubber, not containing fillers Cyclohexane Urea Isophthalic acid Ferronickel Maleic anhydride Ferrochromium nov 3 pct Phthalic anhydride Ferrochrome ov 3 pct. carbon Ethyl methyl ketone Unwrought nickel Chloroform Nickel waste and scrap Carbon tetrachloride Wrought nickel rods and wire Chromic acid Nickel powders Hydrogen peroxide Phenolic resins Polystyrene homo­polymer resins Polyvinylchloride resins Melamine Polystyrene resins and copolymers Acrylic and methacrylic acid resins Ethyl alcohol for nonbeverage use Vinyl resins Ethylbenzene Vinyl resins, NSPF. (4) Modifications to list The Secretary shall add to the list under paragraph (3) substances which meet either the weight or value tests of paragraph (2)(B) and may remove from such list only substances which meet neither of such tests. (b) Other definitions For purposes of this subchapter— (1) Importer The term “importer” means the person entering the taxable substance for consumption, use, or warehousing. (2) Taxable chemicals; United States The terms “taxable chemical” and “United States” have the respective meanings given such terms by section 4662(a). (c) Disposition of revenues from Puerto Rico and the Virgin Islands The provisions of subsections (a)(3) and (b)(3) of section 7652 shall not apply to any tax imposed by section 4671.