Equal pay claims by Brighton and Hove City Council workers have cost more £32 million to settle - and the bill could get even higher.
Up to 3,000 workers were eligible to make claims against the local authority after it was revealed they had been underpaid for years.
Four years after a fighting fund was established for negotiations, The Argus can exclusively reveal the total cost of the “proactive settlements”.
It comes as local authority bosses look to revamp the system of allowances that are paid to up to 75% of its 8,000-strong workforce.
With industrial action a possibility, confidential papers seen by The Argus show finance chiefs fear the council could open itself up to more litigation costs and lengthy disputes if it does not reform its pay structure.
Union representatives said they were aware of the potential issue, adding they had been questioning aspects of the system since the local authority was formed in 1997.
Alex Knutsen, of Unison, said: “We have been telling the council for the past 16 years this could be the case.
“On three separate occasions we have sat down formally with them to discuss it but for various reasons it has been kicked into the long grass.
“We know that any cost to the council is also a cost to staff and the taxpayer which ultimately will lead to jobs.”
In 1997 a national agreement required local authorities to look at different types of terms and conditions and provide a “single status” of employments.
It was intended to bring female cooks, cleaners, care workers and support staff up to the same wages as mostly male refuse collectors and maintenance staff.
Negotiations between unions and the council were supposed to be completed by a deadline of March 2007. A deal for two years' back-pay was initially struck but a series of European judgments meant women were entitled to up to six years' payments.
The Argus revealed in 2009 a fund of £37 million, made up of PFI money and a Government loan, had been established.
Three years on, confidential papers seen by The Argus confirm the amount paid out in “proactive settlements” has reached £32 million so far.
Negotiations between lawyers are still ongoing to settle about 80 unresolved claims.
Union representatives said the total bill could have been even higher if it had not agreed to work with the council to negotiate deals with workers.
The revelation comes a week after councillors handed control of negotiations for reforming its allowance system to officers.
In confidential papers, the local authority said keeping the current structure of payments, which make up 25% of some workers' salaries, would open it up to further litigation.
Bosses also ruled out a phased restructure saying it would lead to “inequalities” and open it up to legal challenges.
The council has set itself a deadline of March to come to an agreement with the unions about changes.
If it fails then it said it will “take all necessary steps” to force through changes by October.
The Argus understands the first preliminary discussion between senior officers and trade union representatives will take place on Tuesday.
Penny Thompson, the council's chief executive, said: “We are committed to negotiations with the unions and will continue to communicate with staff. “We have been clear that this is not about saving money.
“We are working towards a clear and consistent pay package that meets the council's service requirements.”
Mark Turner, of the GMB, said: “We will listen to what they have to say but it depends on what the council wants to do.
“We will not have a gun put to our heads. We are not in the business of cutting people's pay.”
Conservative group leader Geoffrey Theobald said: “The important thing here is to get a fair and equitable system for everyone.”
Labour group leader Gill Mitchell said: “Nobody has an argument with equal pay but these proposals go far beyond that and are being implemented in a way that is bound to be inflammatory.”
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