First Union are publicly campaigning as the four big banks are raking in mega-profits.
They say ANZ, ASB, BNZ and Westpac's profits have increased 80 percent in the past decade- and it's not being passed on to workers or customers.
First Union Policy Analyst Edward Miller says staff and customers alike are suffering from increased net interest margins.
"We represent bank workers, but we represent workers right across different parts of the private sector- supermarket workers, truck drivers, bus drivers, etc. There's lots of workers that are concerned about this."
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