Tata Steel will cut 720 jobs in the UK, it has announced, mainly at its plant in Rotherham in South Yorkshire.
The firm blamed the strong pound and electricity costs which it said were double those in Europe meaning it underperformed in the face of steel imports.
Tata said it had "identified 720 positions which will potentially become redundant" but will 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."
Tata Steel is "very disappointed" by its employees' decision to strike later this month, a spokesperson has said.
"Everyone agrees that changes need to be made to resolve the challenges facing our pension scheme, which has a projected shortfall of over £2 billion.
"We urge the unions and individual employees to think very carefully about the consequences of industrial action."
Representatives of the 13,000 workers at Tata Steel who have voted to strike later this month have said that their company left "no option but to take industrial action".
Roy Rickhuss, general secretary of the Community, said: "The company has not shown any willingness to return to meaningful negotiations to find an end to this dispute. Our members are determined to stand up for their pensions.
"They delivered a massive vote in favour of industrial action, so that is what will happen. An overtime ban and work-to-rule will cause massive disruption to Tata's operations and severely limit production."
Dave Hulse, a GMB national officer, said: "It's time Tata got back round the table and looked for a way to resolve this dispute."
Thousands of workers at Tata Steel are to go on strike in a row over pensions, unions have announced.
The strike, the first in the industry for 35 years, will take place on 22 June, with around 13,000 workers involved in the action.
It follows a decision by the company to close employees' final salary pension scheme
As ITV News Business Editor Joel Hills reports, Community union General Secretary Roy Rickhuss claimed the move had given staff "no option" but to strike.
Tata Steel plans to cut up to 500 jobs in Scunthorpe, Workington and Teesside because of weak demand in the construction industry, the company said today.
Unions have called the news that Tata is cutting 900 jobs "devastating" and said it capped off a "dark" week for the UK economy.
The news follows announcements of further potential and real job losses at Vion, Premier Foods, Standard Life, Comet and Newcastle City Council.
Unite general secretary Len McCluskey said: "Today's news at Tata rounds off a dark seven days for the UK economy."
Michael Leahy, general secretary of the Community trade union, said he was seeking an "urgent meeting with the company to ensure our principle of no compulsory redundancies is upheld".
Announcing 900 job losses and 12 site closures as part of its "transformation strategy" for growth, steel giant Tata said the ongoing European debt crisis had seriously impacted demand.
It said demand for steel within the Euro bloc had fallen by 25% since 2007, and was forecast to slump by another 10% this year.
The company, which employs 19,000 in its steel business in the UK, said it remained committed to investing in the business to help create long-term stability.
A Welsh Government spokesman said today's announcement was "very disappointing news" and "a massive blow" that shows the very real challenges faced by the manufacturing sector.
Tata's European Chief said he today's job losses are part of a "transformation strategy" to make the company capable of succeeding in "difficult economic conditions." Karl Kohler said: