Supermarket giant Tesco is facing a record £4 billion claim for back pay from thousands of female staff, reports BBC News. Up to 200,000 Tesco staff, mostly women, could receive back pay totalling £20,000 if the legal challenge demanding parity with men who work in Tesco’s warehouses is successful. Paula Lee, of Leigh Day solicitors, said the most common rate for women is £8 an hour whereas for men the hourly rate can be as high as £11 an hour. The law firm added that even though female staff earn less than men, the value of the work is comparable. "We believe an inherent bias has allowed store workers to be underpaid over many years,” Lee said. Tesco stated that it worked hard to ensure all staff were paid "fairly and equally".