Unison research of 50 councils found local authorities are spending up to £1.3 million each on private barristers' and solicitors' fees and up to £1.2 million on their own staff's time attempting to resist the fight for fair wages.
Using the Freedom of Information Act, Unison also revealed more than £11.5 million has been spent to obstruct equal pay - a figure the union believes is ‘the tip of the iceberg'.
Dave Prentis, general secretary of Unison, claims it is a "national disgrace" that local authorities were spending so much money on fighting to keep women's wages down.
He added: "What a waste of money. Councils are stuffing money into lawyers' pockets to put off the inevitable. Expensive lawyers are raising tiny technical points and fighting issues the councils have already been advised they will lose.
"Cases drag on for years and women have died by the time legal arguments are resolved. Taxpayers' money is being poured down the drain and low-paid women continue to be underpaid for jobs that society simply couldn't function without."
But according to the Public Sector People Manager's Association (PPMA), more than two-thirds of councils have made firm progress in reviewing their current pay arrangements and, where necessary, putting new pay arrangements in place for all staff.
Jim Savege, lead officer for pay and reward at the PPMA and HR director at Cumbria County Council, said: "Unison's dismay at the amount of money some councils have had to spend on legal fees in helping navigate the complexities only tells part of the story.
Yes, money has had to be spent on legal fees to help councils navigate the complexities of equal pay, and to try to make sense of the ever-changing and conflicting employment tribunal judgements - exactly as many private-sector organisations do when faced with inconsistent or ambiguous tribunal outcomes.
"Quite often the legal activity is to try to ensure the right money is to be paid to the right people - surely something that is reasonable - particularly given this is public money."
Savege explained much of the legal activity has been in response to thousands of equal pay claims that trade unions have bought against councils.
He added: "Would councils have spent money on legal bills for equal pay if they had not had to? Of course not.
"It would be interesting to know what Unison's legal costs have been in bringing all of the equal pay claims and appeals - how many members membership fees have been spent up and down the country by Unison in bringing unnecessary legal action?"
The PPMA is working to support its members in introducing new pay arrangements where necessary, and is lobbying nationally and internationally to seek to get more effective law, tribunal and industrial relations arrangements in place that will make this task easier and more accessible for all.
