You should have a copy of the Union Contract, if not contact your local and have them send you one. You should have gotten one when you started and you should get one every new contract.
Right now it works like this:
You start at 70% of 2002 full rate which was $23.77/hr up here in New England.
then 75% after obataining seniority
then 80% after 1 year
then 85% after 18months
then 90% after 1 and 1/2 years
finally full rate after 2 years. The last bump is a big one because you have not gotten any full rate raises during your progression. Everything is based on the 2002 full rate.
Of course if UPS and the union get their way the length of progression will be even longer.
So much for equal pay for equal work. I remember when progression was 6 months.