In a House of Commons motion, the Tory trade and industry spokesman, Christopher Chope, said reports that the Ford motor company was to put up to pounds 12m into the Dome were cause for concern.
The Director General of Fair Trading, John Bridgeman, has told MPs he plans to investigate car prices in Britain, and a decision on his report could fall to Mr Mandelson as Trade and Industry Secretary. The Tories believe the money could be better spent at a time when Ford might have to lay off workers at its Dagenham plant over the Christmas period.
Mr Chope's motion follows a series of alleged conflicts of interest between Mr Mandelson's roles in the cabinet and the Dome.
Earlier this year he took advice on whether he should step aside from a decision on a merger between British Airways and American Airlines - BA is a Dome sponsor - but decided there was no need.
During the Summer, Mr Mandelson took advice again when it emerged that BSkyB, yet another major backer of the project, was planning a takeover of Manchester United.
Again, he was told there was no need to do so.
The motion, which is expected to be signed by a large number of Tory MPs and possibly some Labour critics of the Dome, said Mr Mandelson had promised "both to act fairly and to be seen to do so".
The minister should explain the basis on which he had concluded he could keep that promise "despite the acceptance by the New Millennium Experience Company, of which he is sole shareholder, of sponsorship from British Airways and BSkyB totalling pounds 24m."
A spokesman for Mr Mandelson said that no sponsorship deal with Ford had yet been announced. If there was a deal, and if an inquiry were launched, the minister would take advice again.
"If there was a conflict he would stand aside but there is no question of one arising at the moment," he said.Reuse content