Asda has lost the first of three stages of appeal against the ruling that store and warehouse workers deserve the same hourly rate.
The decision means that lower-paid shopkeepers, mostly women, can compare themselves to higher-paid warehouse workers, mostly men.
Asda said he was "disappointed" with the decision and said it would remain confident of his case.
The judgment as to whether the work is equally valuable will probably be in May.
In his statement, Asda stated that it had appealed because it involved complex legal issues that had never been fully investigated by the private sector and that we would continue to ensure that this case was given the legal scrutiny it deserved.
Leigh's day, which represented the staff, said the verdict was a "big step forward in the fight for fair pay".
Leigh Day represents more than 30,000 shopkeepers from the big four supermarkets – Asda, Sainsbury's, Tesco and Morrisons – in similar cases.
The lawyer said that claims against the big four supermarkets, if they lose their case and have to pay all eligible employees, could be over £ 8 billion.