Tata Steel is set to cut up to 1,500 jobs at sites in Scunthorpe and Teesside.
It follows a fall in demand for structural steel in the construction industry.
In a statement, the Indian steel giant said: “The decline in some major markets, particularly the construction sector, has been a key factor.
“Demand for structural steel in the UK is only two-thirds of the 2007 level and is not expected to fully recover within the next five years.
“This strategy includes a proposal to close or mothball parts of the Scunthorpe plant and puts at risk 1,200 jobs at Scunthorpe and 300 jobs at the Teesside site.”
Tata is one of the biggest steel makers in the world, with operations in 26 countries.