Lord Mandelson has criticised union Unite for warning a major car plant will collapse without government help.
The union said the slump in car production figures, showing vehicle manufacturing fell 60 per cent in January, is "the greatest crisis to face our car industry".
However, joint general secretary Tony Woodley went further, talking about a specific, but unnamed plant.
"We've got a car plant that, within just a couple of days, would have run of cash and needs serious financial help to stop over 6,000 people losing their jobs," he said.
Another 30,000 jobs in the supply chain would also be affected, Mr Woodley added.
The government needs to take urgent steps to introduce short-term working and inject cash into the car economy to save the plant, Unite said.
The union refused to name the plant, over fears the news could cause a run on shares in the firm that owns it.
However, business secretary Peter Mandelson has attacked the comments.
Lord Mandelson said: "Rumours can very easily turn into a shockwave that destabilises a company or an industry and brings about the very outcome that we are seeking to avoid."
The Society of Motor Manufacturers and Traders, which represents Britain's car industry, said it has no knowledge of any car plant facing imminent closure.
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