According to Unison, £1.3 million each is spent annually on hiring professional legal teams in order to "resist the fight for fair wages", with more than £11.5 million being spent in total.
Using data compiled under the Freedom of Information Act, the union discovered that Sandwell Council has spent £124 per female employee in resisting equal pay.
This is in contrast to some low-paid local authority employees who Unison claims earn £12,145 each year, a comparison it called "shocking".
Brian Critchley, lecturer in employment relations at London Metropolitan University, said: "One of the more shocking things to come out of this exercise is the total lack of coherence among councils on their policy towards equal pay."
He added that this would suggest some councils would rather spend big to "defend the status quo" than "face the inevitable".
A recent study by the Fawcett Society revealed that many women still feel discriminated against in the workplace, due to the trend for their male colleagues use lap-dancing clubs as venues for entertaining clients.
