A total of 174 former Birmingham City Council workers can go ahead with compensation claims over missed bonuses after the council lost a court appeal.
The workers, mainly women who worked in traditionally-female roles, such as cooks, cleaners and care staff, won a ruling over lower pay last November.
The Supreme Court rejected the council's argument the claims should have been made within six months of staff leaving their jobs.
They now have six years to make claims.
Lawyers for the group called the result a "landmark" judgement and said it could have "huge implications" for potentially "thousands" of other workers.
They said the 174 in the group, named the Abdulla Group after the woman whose name was at the top of the list, could be entitled to about £2m between them.
The lawyers said up to another 1,000 former city council employees could also submit claims.
The city council said it would be reviewing the judgement "in detail" before considering its options.
The authority had argued the women should have submitted their claims through an employment tribunal within a six-month time limit of leaving their jobs.
Wednesday's ruling means the women can now seek compensation through the civil courts system.
The city council had challenged November's ruling in the Supreme Court but a panel of five judges dismissed the authority's appeal.
The court heard the women were among workers who had been denied bonuses which had been given to staff in traditionally male-dominated jobs such as refuse collectors, street cleaners, road workers and grave diggers.
For example, the annual salary of a female Manual Grade 2 worker was £11,127, while the equivalent male salary was £30,599.
The court was told that during 2007 and 2008, tens of thousands of pounds of compensation was given out to female council employees who were still working at the council.
More payments were made to women who had recently left who had taken cases to an employment tribunal.
However, these did not apply to anyone who had left the council more than six months before.
The Abdulla Group members' claims date back to 2010 and the six years they have to claim the compensation has been put back to that date.
That means anyone in the group who was still working at the council from 2004 could be entitled to a payout.
Mary Roche, from Yardley, who worked as a home help for the city council for 27 years, said she "could not believe it" when she heard about the bonuses they had missed.
Joan Clulow, 71, from Bartley Green, worked for the city council for 25 years, also as a home help, and said she felt "absolutely gutted" when she heard about the bonuses that had been paid to others.
She said: "The way [the council] treated us is abominable.
"We did everything [in our jobs] - we washed, dressed, cooked, cleaned, got pensions, everything... We were dedicated to looking after those people."
Chris Benson, partner at law firm Leigh Day and Co, which represented the women, said: "For these women it is the end of a long fight.
"They were underpaid for a long time.
"The salaries were the same - the women did earn between £10,000 and £15,000 a year while the men got the same - but on top of that they were offered bonuses of up to £15,000 that the women weren't entitled to and never received.
"The women just want to get paid fairly for the work that they did."
In a statement, the city council said this type of legal challenge had always previously been pursued in employment tribunals because they were "experienced and specifically trained in dealing with such claims".
It said holding cases in civil courts instead of tribunals meant potentially higher costs for the losing party. It added it would not comment further at present.
A government spokesman said: "We are fully committed to equality in the workplace.
"Local government pay is a devolved matter for local councils and they will want to consider this legal ruling carefully."
Sarah Ozanne, an employment specialist at law firm CMS Cameron McKenna, said: "This is a significant development in current equal pay laws, and leaves employers open to the threat of claims long after the employment relationship has ended."
Employment lawyer Lisa Mayhew of Berwin Leighton Paisner, said the decision could have "a significant impact on the City" by making female employees more willing to bring equal pay claims to the High Court.