WASHINGTON (AP) — President Donald Trump is initiating the process of leaving the Universal Post Union, which sets flat rates for international postage.

That's according to two administration officials who spoke on the condition of anonymity because they weren't authorized to speak on the record.

Trump argues that the global shipping treaty benefits China and other countries at the expense of U.S. businesses — making it cheaper to ship packages from Beijing to New York than from San Francisco to the East coast, which particularly benefits Chinese, manufacturers. The officials say the treaty is used by shippers of the narcotic fentanyl to the U.S. from China.

The U.S. is willing to renegotiate the treaty over the next year but will leave the union if no agreement can be reached, the officials said.