Asda are being pursued by the employment lawyers Leigh Day who two years ago won a landmark £1bn supreme court ruling for lower-paid women employed by Birmingham city council.
If pay discrepancies in equal value jobs can be proved, other supermarkets and retailers, such as Tesco, Sainsbury's, Morrisons, Marks & Spencer and John Lewis, could face similar claims. The Asda cases will determine if the supermarket's store staff jobs, which are mainly held by female workers, are of equal value to higher-paid jobs in the company's male-dominated distribution centres. If they win, workers could be entitled to six years' back pay for the difference in earnings.
Until now equal job evaluation has mainly affected local councils, where jobs are assessed and given pay grades. Birmingham alone has so far paid around half of its £1.1bn bill for the back pay settlements to the women – including cleaners, cooks, care workers and school lunch supervisors – who were denied bonuses and attendance allowances given to male road cleaners and refuse collectors.
The Asda parity issue is expected to be heard within the next two months at Manchester employment tribunal. Newman said Leigh Day was representing 414 store staff, most though not all women.
Asda said in a statement: "We are aware of a small number of claims. We pay a fair market rate for the job people do regardless of gender and we don't recognise discrimination in our business."
The precedent for equal pay claims for comparable jobs was set in 1997 when 1,500 Cleveland dinner ladies won a £5m payout.
A national single status agreement was drawn up the same year giving local authorities 10 years to introduce fair and non-discriminatory grading structures. Tens of thousands of mainly female workers in such jobs, however, are still awaiting settlements for back pay. The general and public service unions GMB and Unison said they had 40,000 outstanding cases across the UK, including in Birmingham.
Statistics show 37,400 equal pay cases were brought in 2009-10, 34,600 in 2010-11 and 28,800 in 2011-12.