The halt will take place "until further notice," and follows Trump's order for an additional 10 percent levy on Chinese imports starting Tuesday.

The order, unveiled over the weekend, also eliminated a duty-free exemption for low value packages.

The "de minimis" exemption allows goods valued at $800 or below to come into the United States without paying duties or certain taxes.

But it has faced scrutiny due to a a surge in shipments claiming the exemption in recent years.

US officials pointed to the growth of Chinese-founded online retailers Shein and Temu as a key factor behind this increase -- and Tuesday's halt could delay parcels from both companies from entering the country.

Washington has been looking to tighten the rule, saying the growth in shipments makes it harder to screen goods for security risks.

However, the USPS gave no reason for its pause on Tuesday.

Other retailers like Amazon might also be impacted.