Bosses at the GMB union reacted angrily to the announcement that Asda is to start consulting with staff over potential job losses next year which could total almost 2,500, according to sources.
Areas of work affected by any changes include petrol, bakery and back office roles.
Jobs in the George areas of Asda stores could also be affected, it is understood.
In a statement Asda said: “In a competitive retail market, where customers rightly expect great value and ease of service, we must always look at how we can work more quickly and efficiently for them - and, inevitably, that means we need to consider changing the roles we need our colleagues to do or the hours needed in particular parts of our stores.
“We believe the proposed changes we are consulting on would allow us to do a better job for our customers.
“We also recognise that discussions about potential change aren’t easy.
“If the decision is taken to implement the proposed changes, we would work with our colleagues to look at the potential impact of these proposals on them.”
An Asda spokesman said the consultation is with certain departments in certain stores “so there is no specific geography that we’re consulting in, and currently these are only proposals, so nothing is finalised”.
Gary Carter, national officer of the GMB union, said: “These proposed redundancies are a hammer blow to Asda workers. The timing of this announcement, in the run-up to Christmas, is doubly appalling.
“Asda is performing well and is highly profitable because of the hard work of our members, who are the backbone of the company. GMB will fight tooth and nail for every single job.
“These cuts make no sense whatsoever. Slashing our members’ jobs would hurt the service Asda customers receive.”
It is understood that consultations with individuals at Asda will not start until the New Year and any redundancies will take place in February at the earliest.
The proposals are believed to include combining back office functions such as administration, removing some George desks, changing the format of some petrol stations from kiosk or shop to automated, and reducing the hours of bakery staff and those employed as “front-end hosts”.
Last month, The Competition and Markets Authority launched the second stage of its investigation into the proposed £12bn merger between Sainsbury’s and Asda.