International Brotherhood of Teamsters
The Teamsters are the last of the five biggest labor unions to back Biden.
James Hoffa has been a vocal supporter of Trump's trade moves but says the president hasn't delivered for union members.
Local unions in Pennsylvania say their national leaders seek to implement an agreement they voted down.
UPS drivers were already divided over a plan to create a two-tier pay system, but the way it was passed has made things even more contentious.
WHAT'S HAPPENING
A proposal between the Teamsters and UPS would create a separate category of lower-paid drivers to help deliver your stuff from Amazon.