The closure of gas Energy Centres in Colchester, Clacton and Chelmsford is set to result in 13 job losses.
Almost 1,500 jobs will go nationally when Centrica, the country's biggest gas supplier, closes its 243 high street stores over the next two to six weeks.
Five workers in Colchester and four in both Clacton and Chelmsford are set to lose their jobs, but a spokeswoman said they will be opportunities for alternative employment, redundancy or early retirement where appropriate.
The stores, which sell cookers, heaters and household appliances, will be replaced by home shopping catalogues, and people will be able to buy the same products by mail order.
But, Maxine Nixon, regional industrial officer for the GMB union, has branded the move a "double betrayal of staff".
She explained that last year the staff had agreed to take a pay cut to protect their jobs and keep the shops open, and now felt "badly let down" by the announcement.
Changes had also been made at the Energy Centres, but she said: "We don't believe that the company has given enough time to give all of these changes a fair chance of success."
GMB will now be holding meetings with Centrica in a bid to make the company change its mind and give the new changes more of a chance.
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