The meteoric rise of shopping platforms selling Chinese-made goods, including Shein and Temu, has been fueled by a decades-old loophole that allows cheap products like $10 dresses to land in U.S. mailboxes tariff-free.

This happens thanks to a so-called de minimis rule exempting packages valued at $800 or less from tariffs as long as they're addressed and shipped to individuals. The exemption is open to all retailers but is most heavily used by Shein and PDD Holdings' Temu, and potentially by TikTok's new e-commerce business.

A June report published by a House of Representatives committee estimated that Shein and Temu likely account for more than 30% of all de minimis shipments into the U.S.