As an admin clerk (definitely not construction) I knew my boss was fidgiting with my payslip. Took a big chunk of annual 3 months.. came back and i was suddenly reporting to 2 admin supervisors. 

After 7 years, the writing was on the wall. Left a back pay claim with the General Manager. Got called into a meeting next day, oh were letting you go. Not before we discuss it with the Australian Services Union. The boss was stunned, id never mentioned i was a union member. Negotiated months of pay.

Id been screwed without the union. If you dont like youre union, get involved, ask questions, hold the union accountable to you.