Around 130 jobs are understood to be at risk after a leaked internal memo revealed plans to shut down Flow Energy’s Ipswich office.
On Wednesday, Octopus Energy announced it had agreed to buy Co-Op Energy in a bid to become one of the UK's fastest growing energy suppliers.
The deal means Octopus has also taken control of Ipswich's Flow Energy, which supplies gas and electricity to 130,000 customers, after it was sold to the Co-Op last year.
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While the deal is rumoured to be worth more than £30m and increase Octopus' customer base to more than one million, it will also lead to the closure of Flow Energy's Felaw Maltings base and the potential loss of around 130 jobs in the run up to Christmas.
A Flow Energy employee, who wishes to remain anonymous, said all staff were called to an emergency meeting at the office on Wednesday.
"There's going to be 130 people out of work - everyone is being made redundant", the source said.
"We knew they were looking to restructure and bring in investors but we didn't know they would be shutting down the whole company.
"People are absolutely devastated - they don't have long to find new jobs."
In a memo circulated at the meeting, and shared with this newspaper, Co-Op Energy states there will be a reduced need for staff as "Octopus have invested heavily in technology which needs a lot less intervention by colleagues".
It states: "Regrettably, it is not intended to retain the Ipswich and Walsall sites. A full redundancy consultation process will be carried out for all employees affected by these proposals, and it is intended that the proposed site closures would be managed on a phased basis from proposed completion mid-September to the middle of December 2019."
The employee added: "It's horrible and the fact there has been no mention of the job losses in press releases makes it worse.
"It's all been about the customer and their new energy suppliers but this is about people's lives.
"These people didn't realise at the start of this week they would be out of a job by the end of it."
Octopus Energy, when asked, would not confirm the closure of the Ipswich site.
A spokesman added: "While we expect that there will be redundancies the number of roles affected has not been confirmed."
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