Image copyright duncan carson Image caption Duncan Carson is taking advice from his union after rejecting the new terms

Duncan Carson has just lost his job as a baker at an Asda store near Stoke, but he is preparing to put up a fight.

He is among the Asda workers who have been sacked after refusing to sign up to new contracts, but he aims to take the supermarket to an employment tribunal.

"I think someone should stand up to them," he said. "What is the point in having a contract if they can unilaterally change it?"

Asda gave its workers until midnight on Saturday to agree to new terms, which include unpaid breaks, changes to night shift payments and being called to work at shorter notice.

The supermarket said 120,000 workers had agreed to the deal, and that fewer than 300 had yet to sign up to the new contract.

But Mr Carson, who has worked for Asda for 13 years, said the new contract was "unacceptable".

"I have an appointment with my union officer on Thursday to start the process," he said.

He usually works from 06:00 until noon as a baker, which he says suits him as he is used to working mornings. The new contract means he can be asked to work any hours from 05:00 until midnight.

The move will destroy trust in the business, he says. While the new terms stipulate that Asda must give four weeks' notice of new shift patterns, "what will stop them changing it again?" he asks.

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Asda has extended its deadline to accept the new term by a week, meaning workers who return can do so on the new terms. Those who do not will remain sacked, however.

"We have been clear that we do not want anyone to leave us as a result of this necessary change and so we have written to the fewer than 300 colleagues who have not signed the contract to offer a little more time to sign up and continue to work with us, should they wish," the company said.

It added that it had always been clear that it understood people had responsibilities outside of work and would "always help them to balance these with their work life".

Neil Derrick, GMB regional officer for Yorkshire and North Derbyshire, said his union would offer advice on what legal challenges his members can mount.

"We are working with every individual member with a view to lodging a claim," he said, which might be based on unfair dismissal, sex discrimination or potentially disability discrimination.

Many Asda workers are women who are on part-time contracts to fit in with looking after family members, he added.

"This new contract completely turns that on its head," he said.

'Unfair dismissal'

However, Sarah Crowther, a barrister at Outer Temple Chambers, noted that other retailers had made similar contract changes and that they were perfectly legal.

She said employees that refused to accept the changes had two potential ways to make a claim: unfair dismissal or indirect discrimination.

"Those with two years of qualifying employment could bring a claim for unfair dismissal. In that situation it would depend on whether the tribunal was satisfied that there was a good business reason and that procedurally everything had been done with adequate consultation," she told the BBC's Today Programme.

Ms Crowther added that people "disproportionately affected" by the change such as "those less able to accommodate the flexibility... might have a case, but then it would be open to an employer to justify that".

Last week, Leeds-based Asda said it was increasing its hourly pay rates.

The supermarket said it would raise its basic rate for its hourly-paid retail employees to £9.18 an hour from 1 April next year, following an increase to £9 from 3 November.

In London, which has an additional allowance to reflect the higher cost of living, basic pay will increase to £10.31 an hour.

The retailer, owned by Walmart, acknowledged that the announcement for April pay rises had come earlier that usual.