Union chiefs have accused Asda of exploiting women shop workers in a row over pay.
It's claimed the supermarket giant is paying thousands of female store staff up to £3 an hour less than their male counterparts working in company warehouses.
GMB Scotland insists a 3.6 per cent pay rise given to Asda retail staff at the start of this month affects mostly women, and takes their wage to just £9.66 an hour, the Sunday Mail reports.
However, warehouse workers, mostly men, are still locked in negotiation with bosses, having just rejected an increase of between 6.5 and 7.5 per cent, that would see their pay rise to £11.98 an hour.
The supermarket has been caught up in a legal battle, with female workers claiming they are paid less than their male colleagues.
The GMB insists the offer will further widen the existing gender pay gap.
The bitter row centres on claims women workers are owed up to £8billion in back pay.
Last year thousands of supermarket workers won a major victory at the Supreme Court in the long-running saga. The court upheld an earlier court ruling that lower-paid shop staff - mostly women - can compare themselves with higher paid warehouse workers, who are mostly men.
GMB Scotland's Robert Deavy said: "Asda retail staff are being exploited and undervalued every hour of every working day. Tens of thousands of working women are being paid less than a tenner an hour for their basic rate of pay -- up to £3 an hour less than their male equivalents in distribution.
"Asda need to value their workers properly with a pay increase that tackles soaring inflation and they need to take full responsibility for their chronic sex discrimination by settling their equal pay liabilities, which could easily run into billions of pounds."
Last week the supermarket's chairman Lord Stuart Rose slammed the UK Government for a "tin-eared and slow" response to the UK's cost-of-living crisis.
Rose, who has also headed up M&S, said Chancellor Rishi Sunak should put together a new package to ease the soaring costs for households. But workers have said it is Asda's executive team who have failed to act.
One female retail worker, who works at a store in Glasgow, said: "Asda's management has caused the widening gender gap in pay.
"Workers are petrified to speak up in case it puts their jobs at risk.
"We have staff who can't afford to make ends meet or buy the food they are putting on the shelves. I'm one of many looking for new jobs. Women workers have been short-changed."
While a step towards securing equal pay, last year's Supreme Court ruling wasn't decisive. Female workers and their solicitors will now need to prove their work is of equal value in terms of skills and training and that gender is the key reason pay is different.
Michael Newman, a partner at Leigh Day, said: "Time and time again Asda demonstrates a lack of appreciation for the hard work shopfloor workers do and this is yet another example.
"There is no justification for the difference in pay between shopfloor workers, most of whom are women, and the predominantly male distribution centre staff.
"Leigh Day will continue to fight for equal pay for shopfloor workers."
Asda said: "Retail and distribution are separate and distinct market sectors and the demands of jobs in stores and depots are very different.
"We pay colleagues the market rate in each sector regardless of gender."
