Asda has declined a last-ditch request from unions to remove the threat of dismissal from thousands of staff who will be sacked if they fail to sign compulsory contracts by the end of next week.
The GMB union estimates up to 12,000 of more than 100,000 affected Asda employees could lose their jobs because they are unable to agree to the terms of the new deal, known as Contract 6, which demands greater flexibility from workers.
Asda said the "overwhelming majority" of employees have signed and claimed the deal is in the best interests of employees and customers.
A spokesman described the GMB estimate as "unsubstantiated speculation" but would not confirm how many employees are yet to sign.
The retailer, which is owned by US retail giant Walmart, the largest private employer in the world, says the contracts are a necessary response to competition in the supermarket sector and will leave 95% of those affected with higher pay at a cost of £80m.
Unions say the dispute is emblematic of a new, less-stable world of work, in which employees' terms and conditions are squeezed ever harder by companies under pressure from online retailers and shrinking margins.
Angela Leighton is typical of those affected. She started working at Asda in 1995.
"I was only going to do it for six weeks when the kids were little," she said.
One job led to another and another, and nearly 25 years later she is still there, a community champion in the Crewe branch helping to run local charitable work and, for the last seven years, the GMB union representative.
But next week could be her last.
If she fails to sign Contract 6, she will be dismissed on 3 November.
Angela's daughter Laura faced the same dilemma. She started at the supermarket 16 years ago as a holiday job when she was at college.
Now a single mother of two boys, one of whom has ADHD, she juggles a 16-hour week as a checkout operator with childcare commitments.
Angela often has the kids when she's at work. It's a delicate balance threatened by the new deal that she feels she has no choice but to accept.
"If I don't sign Contract 6 then I'm left without a position and a job, and my children are going to suffer," she said.
Contract 6 was first introduced by Asda as a voluntary change in 2017, but earlier this year it became compulsory.
The GMB, which had initially welcomed the deal, objected, but after three rounds of consultation with staff it was introduced with a deadline of 2 November.
Anyone not signing was put on 12 weeks' notice, free to change their mind at any time knowing that failure to agree by next weekend will put them out of a job.
The biggest problem Angela and Laura have with the new deal is flexibility.
Contract 6 requires staff to be available for any shift demanded by managers, threatening the working patterns of thousands of employees - many of them women - based around children and other care responsibilities.
There are other issues.
Breaks will become unpaid; five out of eight bank holidays must be worked or taken from annual leave; and night-time hours, for which additional pay is due, will be cut from 10pm-6am to midnight to 5am.
In exchange, staff will receive a 79p hourly pay rise, taking basic pay to £9-an-hour, in line with the target national living wage for April 2020.
For Laura, there was an unintended consequence beyond the loss of flexibility.
Making all breaks unpaid turned her 16-hour week into 15-and-a-half hours, dropping her below the threshold for receiving working tax credit for single parents.
That left universal credit her only other option, and she calculates the half-hour reduction would have cost her £400 a month. She negotiated with Asda and was told she would receive 16 hours work if she signed.
Reluctantly, this week she did.
"I felt pressured, I felt like I had no choice but to do it. It's been really difficult, the worry of having two children as a single parent and potentially not having a job, and this contract potentially making me substantially poorer," she said.
Despite having led union opposition and represented staff in meetings with management at the Crewe store, Angela will probably do the same. Her husband is in remission from cancer, and despite having her leave cut from 33 days plus bank holiday to 29, excluding bank holidays, she feels she has little choice.
She says many colleagues will do likewise.
"The number who haven't signed is dwindling every day and to be honest that's purely the fear factor. They're fearful of not having a job at the end of it. I haven't signed mine but I'm going to have to, otherwise I'm not going to have a job."
A spokesman for Asda said: "Throughout the consultation process on these changes we have taken colleagues concerns and feedback from representatives - including the GMB - on board and have been clear that we understand our colleagues have responsibilities outside of work and we will always help them balance these with their work life.
"We have been clear that we don't want any of our colleagues to leave us and whilst the vast majority of colleagues have chosen to sign the new contract, we continue to have conversations with those who have chosen not to, to try and understand their concerns.
"It is vital that we make sure we are prepared to adapt to the demands of our market. Change is never easy, but we are determined that Asda remains a sustainable business for its customers and colleagues - now and in the future."
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