What makes you believe the company wants to retain PT hourly employees? They do everything to make employees quit. Union isn't much help either.
I agree with both of you. In theory, for a job as hard as this, they'd want to keep as many employees on as they can...especially when the hourly rate barely rivals that of McDonald's. In reality, UPS seems to loathe everybody on the operations level...from my perspective anyway.
Just because both the union and UPS want high turnover to be the norm, doesn't mean they're on the same page though. Depending on the local, I don't think the union wants PT employees to last more than a month or so. That maximizes their income from inititation fees ($250, $25/10 weeks in my local) by replacing one new hire with another every month or so. High short-term turnover means they have a constant stream of money coming in.
The company wants PT employees to last between 3 and 9 months, so they can maximize their investment in recruiting and training, but so they don't end up getting their insurance or other paid benefits at the 1 year mark.
Neither seem to be familiar with the concept of "be careful what you wish for."