The US Postal Service (USPS) announced yesterday that it will “temporarily” and “until further notice” not accept packages from mainland China and Hong Kong, amid reciprocal customs tariffs imposed by Washington and Beijing.

“We call on the US to stop politicizing and instrumentalizing economic and trade issues, and to stop putting undue pressure on Chinese enterprises,” Lin Jian, a spokesman for the Chinese Foreign Ministry, told a regular briefing of reporters today.

The USPS did not give reasons for the move in its very brief statement, specifying only that “the flow of letters and flat parcels (with the same origin) will not be affected.”

However, the announcement came in the wake of retaliatory measures taken by Beijing in response to the 10% increase in US customs duties on products imported from China that came into effect yesterday. Beijing then imposed its own tariffs on a range of products imported from the US: coal, oil, or agricultural machinery.

The USPS decision could block, at least temporarily, parcels from particularly popular e-commerce platforms, such as Shein and Temu, that sell low-priced goods, from entering the US.

A worker at the Macau post office told AFP today, however, that parcels can continue to be sent to the US from this special administrative region of China. “For now, we are not affected because (the suspension) only affects parcels coming from mainland China and Hong Kong,” he added.

Low-value items were previously not subject to US customs duties, but Trump’s new administration has suspended that rule in addition to imposing additional tariffs.

This exemption had largely benefited the Shein and Temu platforms as well as Amazon: the number of exempt shipments had increased by 600% over the past 10 years to reach 1.36 billion packages last year, compared to nearly 140 million in 2015.

Reacting to these announcements, shares of Chinese e-commerce companies plunged on the Hong Kong Stock Exchange: shares of JD.com lost 5.6% of their value today. Shein and Temu have not yet responded to requests for comment from Agence France-Presse.

Initially, customs duties (25%) were to be imposed from yesterday on exports from Mexico and Canada to the US. But Donald Trump gave a one-month grace period after making commitments to strengthen border security. Mexico, Canada and China are the US’s main trading partners and together account for more than 40% of imports into the country.