An equal pay case is being taken against supermarket giant Tesco which lawyers estimate could lead to a bill of £4 billion.
Law firm Leigh Day will take the first stage of the claim to the conciliation service Acas this week on behalf of 100 women, claiming they are paid less than men for work of equal value.
The lawyers said the case could eventually involve 200,000 women, making it the largest equal pay challenge in the UK.
Tesco said it works hard to ensure that all staff are paid “fairly and equally”.
Lawyers argue that employees working in the male-dominated distribution centres are paid considerably more than the largely female-staffed Tesco stores, and may earn £11 an hour while the most common grade for store staff sees them receive around £8 per hour.
The disparity could see a full-time distribution worker on the same hours earning over £100 a week, or £5,000 a year, more than store staff, Leigh Day said.
The law firm said it had been approached by more than 1,000 employees and ex-employees of the supermarket.
It claims the case could lead to compensation payments of £4 billion.
Paula Lee, from Leigh Day, who is representing the Tesco women, said: “We believe an inherent bias has allowed store workers to be underpaid for many years.
“In terms of equal worth to the company, there really should be no argument that workers in stores, compared to those working in distribution centres, contribute at least equal value to the vast profits made by Tesco, which last year had group sales of £49.9 billion.
“In the week where we have marked the 100-year anniversary since women began to get the vote, the time has come for companies and public organisations to have a long, hard look at themselves, to see the inequality which is still deeply entrenched in their organisations.”
The claims have been submitted to conciliation body Acas and the move follows similar cases against Asda and Sainsbury’s which are currently being dealt with by the employment tribunal process.
A Tesco spokesman said: “We are unable to comment on a claim that we have not received.
“Tesco has always been a place for people to get on in their career, regardless of their gender, background or education, and we work hard to make sure all our colleagues are paid fairly and equally for the jobs they do.”
The company said it carefully considers any changes to pay in partnership with the shopworkers’ union Usdaw, which is not involved in the case.
Sam Smethers, chief executive of the Fawcett Society, said: “The Tesco pay case is just the latest in a long line of equal-value claims.
“The law says women are entitled to equal pay for doing the same job or for work of equal value. As employers review their pay systems, they should address any pay inequality they find.”
Lauren Lougheed, of Leigh Day, said the case follows similar claims being made by the law firm on behalf of workers in Asda and Sainsbury’s.
The company has been contacted by a number of female Tesco workers and believes thousands will be affected by the new claim, which is likely to go before an employment tribunal after being taken to Acas.
Leigh Day is currently representing more than 20,000 shop-floor workers in equal pay claims against Sainsbury’s and Asda, which both face similar claims of discrepancies in pay between the male-dominated distribution centres
and the mainly female-staffed stores.