National Grid has started consulting with employees on “organisational changes” which may lead to job losses.
The electricity and gas transmission firm said workers would be able to apply for voluntary redundancy.
A statement said: “At National Grid we are constantly looking for ways to deliver an industry-leading service whilst maintaining the lowest cost to bill-payers.
“Whilst we only represent around 3% of the average household bill, we are committed to always looking for ways to operate more efficiently.
“As part of this process, we have begun a consultation with our employees on organisational changes that will help us become an even more cost-efficient and agile business.
“No decisions have yet been made but this may result in redundancies, and employees interested in voluntary redundancy will be able to apply.
“National Grid is focused on delivering energy safely and reliably to our customers and we would like to reassure people that this work to improve our efficiency will have no impact on our ability to deliver a safe and reliable energy network.”
Steve Thomas, national officer of the Prospect union, said: “Our members work tirelessly to ensure that the country’s energy supply continues seamlessly and the scale of these redundancy plans will create great uncertainty for them.
“We will be closely examining the impact that large-scale job cuts will have on the network and how it could be potentially compromised.
“Any changes that take place must be done in consultation with the unions. As the largest union at National Grid, Prospect will be leading discussions to ensure that compulsory redundancies are avoided.
“Prospect will be focusing on members’ views and voices being heard throughout the process and that they remain fully informed during this unsettling period.”