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."