They were cleaners, cooks and carers for the council. They were on the same basic wage as male workers such as refuse collectors and grave diggers, but bonuses the women did not receive saw the men earn on average 10,000 - 13,000 more than the women.
However, scores of women who had left the council fell foul of a rule that say employees must launch tribunals within six months of their leaving a job.
They took their case to the High Court, which found in their favour in 2010 but the council appealed against that ruling.
Today the Supreme Court ruled the council has a case to answer in the High Court.
Lawyers for the group say the claim will cost Birmingham City Council £2 million - and they have another 1000 cases of former council workers who say they were also underpaid.
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Rather cloudy with patchy rain at first. Clear spells developing.