The US has announced plans to withdraw from a 144-year-old postal treaty, which the White House says lets China ship goods at unfairly low prices.
The United Nations treaty sets lower international rates for packages from certain countries, a move originally designed to support poorer nations.
But the US says the discounts put American businesses at a disadvantage.
Officials said they hope the notice of withdrawal will set the stage to agree a better deal.
“We’re looking for a fair system,” a senior administration official told reporters.
“We do hope that ultimately we achieve a negotiated outcome.”
The treaty sets limits for charges on parcels under 2kg (4.4lbs) but the US would like to change the treaty to allow countries to set their own rates for these smaller parcels, as they can for packages over that weight limit, officials said.
The rise of international online shopping has resulted in an increase in small packages being sent via the postal system, and American firms say it can now cost more to post an item within the US than it does to send a similar item from Shanghai to the US.