Here's a good background article, but I worried it was too political to submit directly:

"On October 17, 2018, President Trump announced that the United States will withdraw from the Universal Postal Union (UPU), an intergovernmental organization that sets the rules and rates for international mail delivery. The decision to withdraw has been widely seen as another salvo in the Trump administration’s campaign against what it deems as unfair trade practices benefitting China. This post explains what the UPU is, why the Trump administration is withdrawing from it, the legality of withdrawal, how this decision is related to the trade war with China, and what could happen next."

https://www.lawfareblog.com/withdrawal-universal-postal-unio...