Tata Steel is planning to cut 720 jobs mainly at its plant in Rotherham.
The firm, which also has a plant in Corby, said the business had been underperforming in the face of steel imports due to the strong pound and higher electricity costs which it said were double those of European competitors.
Tata said it had “identified 720 positions which will potentially become redundant” but with work with unions and employees to redeploy workers and minimise the number of compulsory redundancies.
Karl Koehler, chief executive of Tata Steel’s European operations, said: “I realise how distressing this news will be for all those affected, but I am also extremely aware of our responsibility towards the ongoing survival of this business which will continue to employ about 1,500 people in South Yorkshire.”
The GMB union says the Government must ensure competitive tariffs for large scale power users so that the push for low carbon does not drive heavy industry out of the UK.
GMB national officer Dave Hulse said: “The 720 proposed job losses is absolutely devastating news for workers and their families and for the local economies.
“It is a very big blow for UK manufacturing particularly after all the hard work that has been put in by all concerned to bring stability to the business after the dispute about the pensions scheme.
“The GMB will work with the company and others to mitigate the job losses and to avoid compulsory redundancies.
“GMB will want to assess how the UK is losing out due to the weakness of the euro sucking imports into the UK and the extent to which higher power costs here than for EU competitors is leading to job losses.
“Government must ensure competitive tariffs for large scale power users so that the push for low carbon does not drive heavy industry out of the UK.”