Washington will begin withdrawing from a U.N. pact that lowers rates for foreign postal deliveries of small packages in the United States, the latest move by the Trump administration to challenge practices it sees as unfairly advantageous to China.

White House officials said the United States will start the process of getting out of the Universal Postal Union, a Switzerland-based United Nations organization that connects postal services worldwide.

The White House said the UPU enables foreign postal services to take advantage of cheap shipments to the United States, creating an unfair cost advantage over U.S. companies that ship goods, and hurting the income of the U.S. Postal Service.