A "dramatic" employment tribunal victory for a group of women means thousands of workers at supermarket giant Asda can proceed with claims for equal pay.
Law firm Leigh Day said the case is the UK's largest ever private sector equal pay claim. It involved women who felt they were paid less than others in the company despite doing work of equal value.
A judgment by the Manchester employment tribunal following a hearing in June will allow more than 7,000 store workers to press ahead with claims for equal pay against Asda, said Leigh Day.
The case was brought on behalf of a group of women, mainly in hourly paid jobs in stores. They were comparing their pay to mainly male staff in distribution depots.
Lauren Lougheed, a lawyer in the employment team who is representing the claimants, said: "This is a dramatic victory for the workers we represent. Asda tried to argue that because the shops and distribution centres were in different locations, with different pay arrangements, that Asda could pay the men what they like.
"However, the employment tribunal found that Asda, the employer of both men and women, could have made sure that there was equal pay between men and women if they wanted to, but chose not to.
"This judgment will have far-reaching implications on other supermarket equal pay claims including those we are bringing on behalf of around 400 Sainsbury's workers who are in a similar situation."
Leigh Day said claims could see workers recovering more than £100 million, going back to 2002. And it could now be followed by new claims from workers who had been awaiting the judgment.
An Asda spokesman said: "This decision by the employment tribunal does not determine the eventual outcome of the case. It relates to a technical preliminary issue of whether jobs in different parts of the business can be compared.
"The tribunal has yet to consider whether the jobs are of equal value in terms of their demands and if some jobs are, only then will the tribunal move on to consider the reasons for the differentials, including the existence of different market rates in different industry sectors.
"We continue to strongly dispute the claims being made against us. We believe that the demands of the jobs are very different and are considering our options for appeal.
"At Asda, hourly-paid colleagues doing the same job in the same location are paid the same. Men and women doing the same job in our retail stores are paid the same. Men and women doing the same job in our distribution centres are paid the same. Pay rates in stores differ from pay rates in distribution centres for legitimate reasons, including the different market rates for different jobs in different sectors."
Sam Smethers, chief executive of women's rights charity the Fawcett Society, said: "This is great news for low-paid women - a reminder to employers that equal-value claims are covered by the law and will win."