As I recall a labor agreement \ negotiation support document from the NALC or APWU. But I'm old and probably lost it.
If you happen to find it again, it would be interesting to look over it.
K. It supported Usps side to (current situation) make temp positions at $16.85 no OT termed after 360 days because Zon contract pays "x" and if full union labor would pay up to $43