Asda has lost an employment tribunal appeal on equal pay, opening the door to possible legal action.

The hearing related to an October 2016 ruling that women employees, who mainly work in Asda shops, could compare themselves to male staff in Asda’s distribution centres.

The comparison was part of a claim brought by about 10,000 former and current Asda staff, mainly women.

They argued that their work was of equal value to that of their male counterparts.

An appeal by Asda was today dismissed by the Employment Appeal Tribunal.

The GMB trade union said it was a “landmark ruling” and called on the Walmart-owned grocer to become “a market leader in solving this wide ranging industry problem”.

The union said the ruling “opens the door for a potential equal pay claim” but it appeared to be keen to talk to Asda about a solution.

GMB general secretary Tim Roache, said: “GMB look forward to Asda management sitting down and finding a sensible negotiated solution to recognising that our women members in stores should be paid and valued as equal to the men.

“Instead of wasting money on litigation, we ask Asda to be a market leader in solving this wide ranging industry problem.”

An Asda spokesman said: “We are disappointed with this appeal ruling which relates to a technical preliminary issue of whether jobs in different parts of the business can be compared.

”The Employment Appeal Tribunal have given us permission to appeal against this judgment, to the Court of Appeal. We continue to strongly dispute the claims being made against us. The employment 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.

”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.”

Chris Benson, head of the employment and discrimination department at solicitors Leigh Day, which worked with the GMB to bring the case, said: “Asda continues to appeal every point available to them, rather than focusing on paying men in the distribution centres and women in the stores equally, but judges at every level have been adamant that the claims can continue.

“After yet another defeat, we hope that Asda take this opportunity to reflect on the merits of the claims, and concentrate on why they pay men more than women for jobs of equal value, rather than trying to stop the claims going ahead at all.”