Morrisons could face a £1 billion bill as the retailer is challenged in an equal pay dispute.
Law firm Leigh Day is seeking compensation for female employees, who are paid less than the male staff at the supermarket’s distribution centres.
Warehouse workers are paid between £1 and £4 an hour more than their colleagues in shops.
The law firm is currently seeking compensation for eight women but said that an estimated 80,000 employees could be eligible.
It has been estimated that 20,000 people are involved in the Asda case. The supermarket will challenge the ruling at the court of appeal in October.
Emma Satyamurti, a partner at Leigh Day, said: “The big four supermarkets in the UK make vast amounts each year in profits – it is time that they faced up to their legal obligations under equal pay legislation.”
“Our clients believe that those working on the shop floor should be paid the same as those in the distribution centres, and a failure to commit to this is not only unfair but unlawful.
“This legal action is being taken forward to ensure that the work done in stores and distribution centres is recognised as being of equal value; not the same work, but work of equal value and that those working on the shop floor should be paid the same as their colleagues in distribution.”
A spokesperson for Morrisons said: “We are not aware of any court proceedings issued by a third party. We have received a letter asking us a number of questions about our pay policies. Our aim is to pay our colleagues fairly and equally for the job that they do, irrespective of their gender.”
Shares in the group (LON: MRW) are trading at 267,95 (0842GMT).