GENEVA — The United States agreed on Wednesday to stay in a United Nations body that has regulated international mail service for more than a century after delegates agreed during emergency talks to change the way postal fees are structured.
The Trump administration had threatened to leave the body, the Universal Postal Union, after Oct. 17 if its members did not change the system of fees that postal services charge for collection and delivery of international mail and small parcels.
The administration’s primary concern has been the sliding scale of fees that allowed China, the world’s second-largest economy, to take advantage of lower rates that are available to developing countries. As a result, manufacturers in countries like China and Cambodia have been able to pay far less to send a small package to the United States than what it costs American businesses to ship one from Los Angeles to New York.
The deal struck on Wednesday will allow the United States to start setting its own postal fees in July and allow other countries that receive more than 75,000 metric tons of mail a year to start phasing in higher rates in January 2021.
The agreement is less disruptive than what the United States had pressed for, which would have created a pricing free-for-all. This new system sets a volume threshold for countries that can self-declare rates and a number of other controls on the process.
Delegates from about 140 countries stood to applaud as Bishar Hussein, the head of the Universal Postal Union, said the new formula had passed. Only a day earlier, he had warned that a United States withdrawal could lead to chaos in international mail service.
Mr. Hussein called the outcome “the most remarkable day in the history of the union,” a nearly 150-year-old organization that regulates the postal services of 192 member countries.
Peter Navarro, President Trump’s trade adviser, said the decision was a “huge victory for millions of American workers and businesses” and would save the United States between $300 million and $500 million a year.
“We’ll buy less Chinese stuff, buy more from other countries. We will make more in America, and the market will be free of distortions,” Mr. Navarro said. “China is certainly going to pay more for the privilege of shipping to our market.”
On Tuesday, Mr. Navarro told delegates that the United States was prepared to leave the postal treaty if China continued to enjoy preferential rates. The ultimatum reflected deepening impatience in Washington with the global postal system’s failure to keep up with market and economic changes or recognize China’s growth e-commerce market.
Such an outcome could have proved highly disruptive to American consumers and businesses, including American companies that depend on low-cost shipments.
Companies like eBay have criticized the current system as unfair but warned that a United States withdrawal could have disastrous consequences, particularly ahead of the holiday season. The company had urged the United States to reach some type of agreement and on Wednesday said it supported the outcome.
“The agreement comes at a critical time, when shippers need stability ahead of the upcoming holiday season,” eBay said.
On Wednesday, Mr. Navarro said the agreement would “transform an antiquated, discriminatory system into a modern and resilient one far more prepared to meet the new demands of e-commerce.”
He and American manufacturers said the change would also help curb illicit and counterfeit imports from China by making their shipment more expensive.
The new system will “help protect manufacturers from counterfeiters and other bad actors operating in countries like China, which have been exploiting a dangerous and unfair system,” Jay Timmons, president of the National Association of Manufacturers, said in a statement.
Mr. Navarro had arrived in Geneva calling for the union to switch to a system that would have allowed any country to decide its own fees. That option, which he acknowledged would be the most disruptive, was voted down on Tuesday.
Mr. Hussein had started talks with the United States and other key actors in the process over the weekend but acknowledged by Monday night that “there were moments when I really felt things were falling apart.” The terms of a deal emerged only after another round of hard bargaining among a “convergence group” of 34 countries from different regions, including China and the United States, that ran late into Tuesday and resumed early Wednesday.
As part of the agreement, the United States will also pay $40 million to the postal union over a period of five years. The funding will help the postal union promote the use of computerized systems that provide security against shipments of drugs like fentanyl and other dangerous goods, said David Dadge, a union spokesman.
Mr. Navarro claimed the outcome as victory for “a new brand of Trumpian diplomacy” asserting the principle that international organizations like the postal union had to “respect the rights of the United States and serve their members rather than be used as piggy banks for bad-actor countries that seek to bend their rules.”
Ana Swanson contributed reporting from Washington.