A union has claimed a Thai steel company is interested in buying the Corus steel plant, potentially saving thousands of jobs.
Community urged Corus to "come clean" over the future of the Teesside Cast Products (TCP) site in Redcar.
The factory was partially mothballed earlier this year after an international consortium pulled out of a contract.
A Corus spokesman said it would not confirm or deny the claims.
About 1,600 workers lost their jobs when the factory closed.
According to Community, 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. It said it did not know whether SSI had made a formal bid for the business.
General secretary Michael Leahy said: "Community wants Corus to come clean about what is going on. Thousands of jobs depend on finding an alternative future for Teesside Cast Products.
"The rumour mill just creates more uncertainty for the workforce and their families - it's a disgrace that Corus is keeping everyone in the dark over this issue and treating the people of Teesside with contempt."
Geoff Waterfield is the multi-union chairman. Speaking of the Thai steel company rumoured to be interested in the site, he said: "They're a well established site we've sold steel to them before. There's no reason why we wouldn't fit into their jigsaw puzzle."
A Corus spokesman said: "We have stated often in the past that we are pursuing every opportunity that arises and are open to bids.
"These kind of processes have to take place out of the spotlight if they are to have a serious chance of success."
The process involved due diligence, which routinely led to facility visits, all under conditions of confidentiality, the firm said.
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