Asda workers claim they've been forced to turn to food banks to feed themselves.
Supermarket staff say soaring price rises and below-inflation pay increases have stretched their income to breaking.
A worrying cost-of-living survey of 800 store workers unearthed a catalogue of growing concerns, with more than 500 warning it is affecting their mental health, the Sunday Mail reports.
The details emerged as the latest accounts for the UK's biggest retailer reveal a massive £368 profit in 2020.
More than half of those who took part in the survey said they borrowed money from friends and family to get by.
About five per cent admitted to taking time off because they couldn't afford to travel to work and another seven per cent said they had used food banks.
Almost all (760) said they didn't feel valued as a key worker by the firm.
Among those who completed the survey was Bishopbriggs Asda worker Diane Brownlee, 41.
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The mum of one, who has worked for the supermarket for 11 years, said: "Asda has made record-breaking profits since the beginning of lockdown, with directors paying themselves eye-watering bonuses.
"Workers have been putting their lives on the line by going into work throughout the pandemic. But our hard work hasn't been recognised. We kept people fed during the pandemic.
"With the pay increase, I can no longer afford to work in Asda. And I certainly can't afford to shop there without my staff discount. Asda bosses told us we are frontline staff. But many of us feel like we are on the breadline."
Asda's 123,000 staff were told earlier this month wages would go up to £9.66 an hour from April. But that is much lower than most other supermarkets.
Aldi, Lidl, Morrisons and Sainsbury's all pay their staff over £10 an hour.
Only Tesco pay less - £9.55 an hour -although this year's pay increase is yet to be announced.
Another Asda worker in Blantyre, who wished to remain anonymous, said she had been stunned by price increases.
The gran, who is in her 60s, said: "I have colleagues in their late 60s and even 70. They are working because they can't afford to stop. The pay increase is insulting to the work they do. We get a 10 per cent discount to buy Asda goods but, even with that, it's a struggle.
"I have had colleagues who have been unable to get to work because of the cost of travel. It's very sad."
Asda was bought from US firm Walmart in 2020 by billionaire brothers Zuber and Moshin Issa, from Blackburn, for £6.8billion.
GMB has criticised Asda's below-inflation increase of 3.25 per cent. The consumer price index (CPI) - the Government's preferred choice of measuring the cost of living - is forecast to hit eight per cent by April.
Scotland organiser Robert Deavy said: "Asda bosses should be shamefaced at the prospect of staff being unable to afford the food they stock on the shelves and any politician worth their salt should be stunned - there is no 'levelling up' or 'fair work' in Asda.
"For the last two years staff have been told they are key workers, they've helped keep the country fed and watered throughout the grip of Covid-19, yet after everything they've done for all of us, their 'thank you' will be a wage of just £9.66 an hour while inflation soars to a 30-year high.
"Without intervention, these daily struggles are only going to get worse and for tens of thousands of key workers in Asda it is a real possibility they'll go from the frontline to below the breadline in 2022."
The CPI and cost of food in supermarkets has been brought into sharp focus by food campaigner Jack Monroe over the last month. She forced Asda to roll out its value range to more stores after she showed how prices were rocketing.
In a viral thread on Twitter, the mum said a bag of the cheapest pasta had gone up from 29p to 70p over a year, with canned spaghetti going up from 13p to 35p over the same time.
Monroe started a campaign for statistics to better represent the rising cost of food for the poorest. She has set up her own index tracking the price of the basic ranges at supermarkets with the help of her Twitter followers.
Last month it was announced the Office for National Statistics planned to use supermarket scanner data to give a more detailed picture of price changes.
A spokesman for Asda said the pay deal, done with union Usdaw, would result in wages in excess of £10 an hour within two years.
He also said Asda was the only supermarket to give staff a bonus.
He added: "This pay offer was negotiated with Usdaw and will see colleague hourly pay increase by 7.35 per cent over the next two years, with rates rising to £9.66 in April and to £10.06 next year.
"We are the only supermarket to pay store colleagues a bonus, worth an average of £413 this year for full-time colleagues, as part of a comprehensive benefits package, which also includes 10 per cent discount in store and online."
