https://www.cnbc.com/2018/04/05/amazon-and-ups-disagree-postal-regulatory-commission-public-filings-post-office-cost-structure.html

President Trump isn't the only one questioning the post office's pricing strategy.

UPS, the shipping giant, has been in a back-and-forth with Amazon in recent years over the post office's cost structure, which has direct impact on how the Postal Service sets its package shipping prices, according to public documents filed with the Postal Regulatory Commission (PRC).