Tata Steel has announced that proposed cuts will affect mainly management and administrative roles at sites in Scunthorpe, Teesside and Workington.
David Hulse, national officer of the GMB union, said the news had been a surprise.
"This terrible news has come straight out of the blue. It is a shock to the workforces in Scunthorpe, Workington and Teesside.
"GMB is bitterly disappointed as earlier this year we saw 1,000 people leave the company and everyone involved has worked hard to make all-round improvements.
"GMB will insist on no compulsory redundancies and to bring the number of job losses down."
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Kerrie Gosney brings you Sunday night's forecast
The party leader said her MPs may be in a position to act as deal makers - and they would refuse to allow an exit from the EU.
Rain spreading east Sunday. Decent day on Monday, more changeable thereafter