Supermarket giant Asda is facing legal action from up to 19,000 women over equal pay.
Law firm Leigh Day said the claims were launched after investigations revealed some store employees were being paid less than colleagues doing the same job in its distribution centres.
The pay difference between shop workers, who are mainly female, and warehouse workers, who are mainly men, could be as much as £4 an hour.
If the claimants are successful, they could be entitled to six years' worth of back pay in compensation.
Michael Newman, a discrimination and employment law expert at Leigh Day, warned the implications of these legal claims were "enormous for Asda and many other supermarkets in the UK".
The challenge is thought to be the largest challenge of its kind in the private sector and could act as a "test case" for other retailers.
An Asda spokesman said they would "robustly defend" the claims.
Fashion designers Domenico Dolce and Stefano Gabbana have been cleared of hiding hundreds of millions of euros from Italian tax authorities by the country's top court.
The Italian pair appealed the suspended 18-month jail sentence that had been upheld earlier this year for tax evasion charges.
The star designers were accused of using a Luxembourg holding company, Gado, to avoid paying taxes on royalties of about 1 billion euros.
Today's verdict, reported by Reuters, overturns the guilty verdict first delivered in 2013 and upheld by an appeals court in Milan in April.
The new chief executive of Tesco has said shoppers can expect "positive surprises" as he gets the supermarket back "to what made this business great".
Dave Lewis told ITV News Economic Editor Richard Edgar that the accounting scandal that has enguled Tesco was "not at all what I envisaged when I took the job".
But he stressed that the company's 320,000 staff had continued to do a "stunning job" throughout the recent difficulties.
Spending in British supermarkets has been "essentially flat" since May of last year, according to the Office of National Statistics (ONS).
According to the ONS 'non-specialised food stores' such as Tesco and Sainsbury's account for the vast majority of food spending.
Food spending accounts for 40% of all retail sales in the UK, the ONS added.
This marks a contrast from the years leading up to 2013, where growth in spending has been strong, with a particularly rapid surge between 2006 and 2009.
Some of that previous growth may have been accounted for by food price inflation, as customers's spending has risen despite the quantity of goods they buy remaining more or less the same.
Tesco has said no bonuses were paid to its executives during the period that a huge accounting error took place.
No bonuses were paid during the three years under this review - hence 'no personal gain,' from the accounting mis-statements - Tesco
The company overstated its profits for the first half of this year by £263m, with Tesco CEO Dave Lewis saying the mis-statement was due to booking income in the wrong accounting period.
Tesco boss confirms the £263m accounting error was down to booking income and costs in the wrong periods. But he won't say any more.
Supermarket giant Tesco is withholding payments for its former chief executive, Phil Clarke, as an investigation into overstating profits continues.
The company announced today that it had overstated its profits for the first half of this year by £263m, slightly higher than the £250m originally estimated.
Tesco withholds payments for former CEO Phil Clarke and former finance chief while investigation continues, says new boss.
No evidence that anything around the accounting was "for personal gain" says Tesco's Lewis - but what about bonuses as execs hit targets?
Tesco's boss: "we were the best supermarket for customers and we will be again" ... but they're not now.
Tesco chief executive Dave Lewis has insisted the company will recover from "real challenges" to become "the best supermarket for customers" once more.
Tesco boss, Dave Lewis, now talking to journalists. "We have some very real challenges" but says he won't go into detail about investigation
Tesco has scrapped its full-year trading profit outlook as its domestic sales fell sharply in the second quarter of this year.
Results announced this morning showed underlying UK sales own 5.5% over the period.
The group said last month it had overstated its first-half profit forecast by £250 million pounds, but the group said on Thursday this had now risen to £263 million.
Tesco chairman Sir Richard Broadbent has announced he is stepping down from his role.
The supermarket has recently appointed a new chief executive, Dave Lewis and a new finance director, Alan Stewart.