Wow. OP, thanks for the info.
Honestly, IMO you have to make this as much of an unprofitable decision as possible:
1. Refuse to use UPS for any shipment. Especially those that have nothing to do with firearms. Do everything to hit them where it hurts. Yeah, I know that they are all following suit.
2. Write your GOP Senator and Congressman. I'd be willing to bet that they may have some ideas how to make this more expensive for these companies. They can definitely make USPS hurt.
Most companies just want to turn a profit. Usually the best thing to do to undo this sort of change is to make it as unprofitable as possible.
