Fife Council has been warned it could face a £5m bill from a new round of equal pay claims.
The GMB union has launched legal action on behalf of 30 women and says more could be due more than £2,000 each in lost earnings.
The council has already settled more than £82m worth of claims of historic inequality since 2004.
The new claims of sex discrimination stem from the council's interpretation of a job evaluation review which resulted in substantive rates of pay not being carried forward into employees’ new grade.
According to the union, most of the cases involve jobs mainly held by women home including carers and caterers in care homes and schools.
Helen Meldrum, GMB Scotland organiser, said: 'At a time when second wave equal pay claims are still being settled, a third wave of pay discrimination is opening up because of the council’s interpretation of its job evaluation process.'
The council's chief executive Steve Grimmond said: 'We have received a letter raising some concerns in relation to the implementation arrangements associated with recent job evaluation work.
'All of our arrangements have been progressed in conjunction with local trades unions but we are also happy to engage with national trades unions on this matter and will be following this up.'