The U.S. has been importing about three million parcels a day with little customs inspection, raising concerns about the ease of sending fentanyl.

The U.S. Postal Service’s decision may block or delay parcels from retailers including Shein and Temu from entering the United States.

U.S. President Donald Trump this week shut a trade loophole that has been used to ship low-value packages duty-free from China, the "de minimis" exemption on import tariffs. Trump's halt to Section 321 de minimis is part of his implementation of an additional 10% tariff on China and 25% tariffs on Canada and Mexico,