Supermarket giant Tesco is facing Britain's largest ever equal pay challenge with a bill potentially running to £4 billion, a law firm claims.
Leigh Day has launched legal action against the company on behalf of shop assistants who claim they are paid up to £3 an hour less than their male warehouse workers.
It said distribution centre workers - who are predominantly male - earn in excess of £11 an hour, compared to the largely female-staffed Tesco stores where the common grade sits at £8 an hour.
The disparity could see a male distribution worker earning £5,000 more a year than a female worker doing the same hours, Leigh Day said.
Tesco said they work hard to ensure all staff are paid "fairly and equally".
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 £49.9bn.
"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 it follows similar claims 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."