At the SITC heading level, T-shirts and singlets are grouped together regardless of underwear or outerwear designation. At the HTS 10-digit level, however, some subheadings distinguish between underwear and other T-shirts, which can affect the applicable duty rate. The garment's construction, labeling, and marketing context are all factors CBP may consider when making this determination.

CBP frequently flags T-shirt shipments for fiber-content discrepancies (e.g., a garment declared as 100% cotton that tests as a cotton-polyester blend), undervaluation relative to market benchmarks, and country-of-origin issues where substantial transformation is claimed in a third country. Maintaining mill certifications, accurate cost documentation, and clear production records helps importers defend against these challenges.