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.
“As a consequence the business has proposed a plan to further reduce costs, focus on products that create value and improve its ability to respond quickly to demand fluctuations.
“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.”
A 90-day consultation process is due to start soon with affected employees and union representatives.
Tata is one of the biggest steel makers in the world, with operations in 26 countries.
