Birmingham City Council is to appeal against a recent landmark ruling over equal pay.
A tribunal ruled in April it discriminated against about 5,000 female workers over bonuses paid to male workers on the same pay grade.
The council says it has already done enough to address the outdated system.
But unions estimate the ruling could cost the council up to £80m in back pay to the women, who worked as cleaners, cooks, care assistants and caretakers.
Councillor Alan Rudge, the council's cabinet member for equalities, said the issue considered by the tribunal related to historical bonus schemes abolished in 2008.
He said the authority had since introduced a revised pay and grading structure in line with the Equal Opportunity Commission's guidelines.
He told BBC Radio WM: "We now have an audit, independently taken, in which they confirm that for the first time ever the council has now reduced overall gender pay gaps."
But solicitor Alan Cross of Alan Cross Solicitors, who represented 900 of the women, accused the council of "saying one thing and doing another".
He said: "At the tribunal there was evidence numerous payments were made to the men just for turning up to work.
"They called it different things but it was essentially an attendance payment," he said.
"Yet they had pleaded a legal document saying 'We don't pay attendance payments'."