The plant on Teesside is to be partially mothballed
Union leaders have stepped up warnings of industrial action to try to save jobs at the Corus plant on Teesside.
The plant is to be partially mothballed later and 1,600 workers face losing their jobs.
Business Secretary Lord Mandelson visited the steel plant in Redcar on Thursday and pledged the government would do all it could to save it.
The Community union confirmed moves to ballot its members, while the GMB union announced it was considering action.
Corus confirmed it would start mothballing the Teesside Cast Products site in Redcar, blaming an international consortium for pulling out of a contract halfway through a 10-year deal.
After meeting union representatives, Corus management and Redcar Labour MP Vera Baird on Thursday, Lord Mandelson told workers the government was "fully behind" them.
Before a meeting of the Cabinet in Durham, Prime Minister Gordon Brown said: "I understand the frustration that people feel. There are wonderful workers at Corus.
"This is a good company, this is not a company that should be going under, but we have a problem."
He blamed falling global demand for steel, decreasing prices and, in particular, the international consortium that pulled out of a deal to buy the plant's output.
A "credible" consortium was said to be considering an 11th-hour bid for Redcar and there were suggestions that at least two companies were interested in a possible sale.
Keith Hazlewood, of the GMB, said he had written to the the union's general secretary seeking permission to ballot members of the steel industry.
He said "Corus and the government need to be more pro-active in examining the possible deals on the table to keep this plant open.
"We need an urgent meeting with the prime minister and for him to step in and take charge."
Unite's national officer Terry Pye said the mothballing of the plant was a "disgraceful charade".
He said: "We are aware that serious offers have been made to Corus that would allow production to remain at the plant, but the management has dismissed them all out of hand."
Michael Leahy, leader of the Community trade union, said Tata Corus had "a moral and social responsibility" to the workforce and to Teesside.
A Corus spokesman said: "Corus's position remains unchanged. This is a mothballing, not a permanent closure. TCP will be kept ready for a restart. Corus remains open to credible offers for TCP."