For most textile and fabric imports, US Customs and Border Protection applies the 'substantial transformation' test, or for certain products, specific tariff shift rules under applicable trade agreements. The country where the fabric was woven or knit is often — but not always — the country of origin; further processing such as dyeing or finishing may or may not confer origin depending on the specific rule applicable to that product.

Importers must provide accurate fiber content by percentage on commercial invoices and ensure that finished goods are labeled in compliance with the Textile Fiber Products Identification Act, which requires disclosure of generic fiber names and percentages. Misrepresentation of fiber content can result in CBP penalties and FTC enforcement action.