Energy giant Npower has announced plans to restructure its UK business, leading to a loss of up to 4,500 jobs and the closure of a number of call centres.
Workers at the Swindon-headquartered firm were informed of the decision on Friday (November 29). Redundancies will be made over two years, mainly at call centres.
The largest – in Sunderland – employs 2,000 staff. There are also call centres at Swindon, Birmingham, Hull, Leeds, Oldbury, Solihull, and Worcester.
The news was described as a "body blow" by unions, especially coming just weeks before Christmas.
Johannes Teyssen, chief executive of Npower's new French owner, E.ON, said: "The UK market is currently particularly challenging.
"We've emphasised repeatedly that we'll take all necessary action to return our business there to consistent profitability.
"For this purpose, we've put together proposals and already begun discussing them with British unions."
E.ON's UK chief executive, Michael Lewis, added: "With Npower becoming part of the new Eon - creating the second largest supplier in the UK - we need to build a sustainable business with a lower cost base that allows us to compete in this extremely challenging market.
"We are proposing a number of steps to create an E.ON business that can be both sustainable and successful for the future whilst also fully supporting and serving our customers today.
"For Npower and its employees, these proposals will mean significant changes. We're aware of the impact these proposals will have and there will be appropriate levels of employee support at this time.
"Npower will now consult and work with with trade unions and employee representatives on all these proposals and we are committed to mitigating impact on colleagues. The background to these decisions is of course the unprecedented upheaval in the energy market.
"In the last 18 months we have seen almost one third of suppliers going bust or continuing to operate at a loss."
Unions described the news as a "cruel blow" – especially as it came in the weeks before Christmas.
Unison general secretary Dave Prentis said: "This is a cruel blow for Npower employees. They've been worried about their jobs for months. Now their worst fears have been realised, less than a month before Christmas.
"The UK energy market is in real danger of collapse. If nothing is done, there could soon be other casualties.
"Npower's demise means there's no time to waste. It makes the powerful case for bringing the retail arms of the Big Six energy firms into public ownership.
"This would preserve jobs, ensure customers get a better deal and allow the UK to meet its carbon neutral targets."
The GMB union blamed poor management.