Have you signed a dues checkoff authorization form? UPS can only take dues automatically out of someone's check if the Local Union adds that someone to the monthly list the Union sends UPS. In effect, the Union "bills" the employees, and UPS withholds the money from all of their checks and remits it to the Union. But the Union and UPS must have your permission first.
Dues are taken out monthly or weekly usually starting after thirty days. You will probably owe back dues (and the Initiation Fee) if you have fallen through the cracks thus far.
Initiation Fee gets paid first, then back dues and then current dues. The Union will probably have $25 or so withheld from each weekly check until you are caught up.
If you are in one of the 22 Right-To-Work States, you don't have to join the Union or pay Initiation Fees or dues. Maybe that's why dues haven't been deducted?