UK supermarket chain Asda, owned by US giant Wal-Mart, faces legal action from hundreds of its staff in a dispute over equal pay.
Law firm Leigh Day said it was approached by more than 19,000 people following the announcement that they were taking the legal action over equal pay at the retailer.
It confirmed it is working through the enquiries and is representing hundreds of former and current employees of the supermarket chain, mostly female, who feel they have been paid less than others within the organisation despite carrying out roles of equal value.
Michael Newman, an employment lawyer at Leigh Day, said the claims are possible after investigations revealed employees in the Asda-owned distribution centres were paid more than staff working in the supermarkets themselves.
The law firm said if the case against Asda, which has a 175,000 strong workforce, is successful, claimants may be entitled to six years' worth of back pay to compensate for the difference in earnings.
"In the supermarkets the check-out staff and shelf-stackers are mostly women," Newman said.
"The people in the warehouses are pretty much all men. And, as a whole, the group that is mostly men gets paid more.
"Our investigations suggest that the jobs are pretty much the same, in that warehouse staff are responsible for taking items off shelves, putting them on pallets and loading them into lorries.
"In the supermarket, they do the reverse: taking the pallets off the lorries, unstacking them and putting the items on the shelves. Where the jobs are not similar, we still think they are of equal value."
But Asda said it would "robustly defend" the potential legal action and claimed it does not discriminate against its workers.
"A firm of no win, no fee lawyers is hoping to challenge our award-winning reputation as an equal opportunities employer," a spokesperson for Asda said.
"We do not discriminate and are very proud of our record in this area which, if it comes to it, we will robustly defend."