Unions are seeking urgent talks with npower after the energy giant confirmed plans to axe 2,400 jobs amid heavy financial losses.
The company, owned by German group RWE, ended days of speculation by confirming that its 11,500 strong workforce will be reduced by a fifth, spread across its UK business.
No jobs will be lost at power stations, but retail centres will be hit, and the firm confirmed the closure of a site in Burton, with the loss of around 200 jobs.
The two main RWE businesses in the UK made an aggregate loss of £154 million in 2015 - £99 million at npower and £55 million at RWE Generation.
A two-year recovery plan was announced to deliver a "robust business" built on lower costs, simplicity, high-quality customer service, and ready for the challenges of the future.
A statement said: "Npower takes its responsibilities to its employees seriously and will consult fully with affected employees and with unions over its proposals for the future of the business."
Paul Coffey, chief executive of RWE npower, said: "Npower results continue the trend seen earlier in 2015, but they are nonetheless extremely disappointing and we are starting a two-year process to fix them.
"They show a business that tried to do too much, too soon, while not focusing enough on the fundamentals in a constantly changing market. This led to over-complicated processes and procedures resulting in unhappy customers, too many complaints and extra costs to put things right.
"These issues are not insurmountable. Over the past few months, we have looked at every part of npower, and over the next two years we're fundamentally changing how the company operates."
Unison general secretary Dave Prentis added: "Npower bosses are compounding the anxiety for staff by refusing to meet the unions nationally to discuss this so-called recovery plan and to talk about how to protect jobs and avoid compulsory redundancies.
"We're calling for an emergency meeting so we can work jointly on finding a way out of the mess the company currently finds itself in."
Unite, which represents meter readers, revenue protection officers, gas fitters and electricians, warned npower against "self-defeating" cuts.
National officer Kevin Coyne said: "Confirmation of these job losses on this scale is a bitter blow for workers, their communities and the wider energy sector.
"Npower's ability to repair its tarnished image and keep the lights on for its customers will hinge on a workforce which has worked hard over the past year to turn the company around."
Eamon O'Hearn, GMB national officer, said: "It is disappointing that hard-working members, many of whom have experienced significant disruption and uncertainty over the past 12 months, are set for yet more uncertainty over the next 12.
"The company has failed to clarify where any job losses are likely to occur, meaning that members will go home tonight none the wiser.
"RWE's German workforce would not be treated in this manner."
Energy and Climate Change Secretary Amber Rudd said: "All job losses are regrettable and I have every sympathy for the people who are affected by them. Support will be available from Jobcentre Plus to help those facing redundancy move into new jobs as quickly as possible.
"It's really important that consumers are able to trust the energy companies and know they're getting a good deal. That's why we're promoting more competition and switching so that energy companies realise they have to put their customers first."