Asda is facing the prospect of strike action unless it makes significant concessions on its self-styled “efficiency” plans that have placed thousands of jobs at risk, a union source has told Sky News.

GMB representatives met late on Thursday – hours after Asda revealed a set of proposals that mainly involved moving away from some higher-paid nightshift work.

While 211 night shift managerial roles were placed at risk under the plans, the biggest change would see 4,137 hourly-paid workers move to daytime roles, resulting in the loss of their night shift pay premium of at least £2.52 per hour.

Asda said its planned changes reflected shifting customer habits and a desire to operate as efficiently as possible.

The GMB, which has been a long-time critic of the debt fuelled takeover of the chain in 2021 by the Issa brothers and TDR Capital, has declared the plans as “unworkable”.

It argues that many of those being asked to change hours would be unable to take the pay hit because of the cost of living crisis.

The union also said it placed additional logistical difficulties on staff as the revised shifts would finish at midnight.

The source added on Friday that a significant proportion were expected to take redundancy under the plans as they stand.

But they said there would be a constructive approach to the official consultation period and talks would aim to secure concessions from management to avoid the prospect of any strike ballot.

National officer Nadine Houghton said in a statement: “Many Asda workers feel this is just a cost cutting measure, needed to alleviate the financial pressure of the debt leveraged bonanza to buy Asda – but it’s going to hit some of the lowest paid retail workers on the high street.

“These changes to night-time replenishment have outraged night workers, who will now lose between £300 and £500 a month.

“Many say they will not be able to afford to take the new hours being offered due to the loss of night enhancements and hours. We could see significant job losses.”