The Prime Minister was today urged to make a pre-election intervention to help save thousands of jobs being lost in the mothballing of a giant steelworks.
The Community trade union has urged Corus to "come clean" over the future of the Teesside Cast Products (TCP) site in Redcar, after claims that a foreign company wants to buy the site.
The plant was partially mothballed earlier this year after an international consortium pulled out of a contract.
Around 1,600 workers lost their jobs but Community warned that thousands more employees in other firms across the North East depend on the huge plant.
The union claimed interest in buying the factory had been expressed by Thai steel company SSI.
Community said it understood that SSI visited the TCP plant last Thursday but the union claimed it is in the dark about whether SSI made a formal bid for the business.
General secretary Michael Leahy said he had contacted Gordon Brown and Business Secretary lord Mandelson, urging them to make Corus reveal if there had been a formal takeover bid.
He said he also plans to speak to Ratan Tata, chairman of the Tata Group, which owns Corus, in a bid to seek information.
He said: "It looks more and more like Corus aren't being straight with the TCP workforce and the people of Teesside about whether they have received a bid from SSI or any other party to purchase TCP and preserve steelmaking and thousands of jobs in the wider community.
"Two weeks ago Kirby Adams, Corus chief executive, in the presence of senior Corus executives, told Community, in answer to a direct question, that there were discussions, but that there had been no firm offers for TCP. Now we hear that SSI may have had a bid on the table when he gave his answer.
"Subsequently he refused to give a written assurance that Corus had not received a bid. Just what is going on?"
Community demanded to know if Corus had received any formal bids for the plant and why any potential buyer had not met unions or the Government.
The union also questioned why the factory was mothballed and 1,600 workers made redundant if a competitive bidding process for TCP was going on.
Mr Leahy added: "The people of Teesside and the TCP workforce have a right to know whether Corus is serious about selling TCP or not.
"That is why I have contacted Lord Mandelson and the Prime Minister and asked them to make Corus come clean on the alleged TCP takeover bid by speaking directly to Tata and SSI to find out what is going on and let the people of Teesside know."
Corus has said it continues to engage with potential investors and is open to offers for TCP.
The process involves due diligence, which routinely leads to facility visits, all under conditions of confidentiality, the firm said.
A Corus spokesman said: "As we have made clear many times, Corus continues to engage with potential investors and to be open to offers for TCP.
"The process involves due diligence being done, which routinely involves facility visits, all under conditions of confidentiality.
"Any attempt to undermine this confidentiality in the wholly mistaken view that it might help the process, is on the contrary highly irresponsible and potentially damaging to both the process that is under way and the confidence of potential investors."