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.