A pressure group led by the broadcaster Michael Crick, called Shareholders United Against Murdoch, claims to have tapes proving that a helpline set up by BSkyB to advise Manchester United shareholders on the offer is giving inaccurate advice.
SUAM alleges that the helpline's advisers do not make it clear to callers that they do not have to accept BSkyB's offer for their shares.
The allegations come amid mounting opposition to the takeover. The Office of Fair Trading is currently investigating whether to recommend referring the bid to the Monopolies and Mergers Commission. It is due to pass its recommendations to Peter Mandelson, the Secretary of State for Trade and Industry, on 2 November.
BSkyB has offered Manchester United shareholders three different forms of payment - cash, loan notes and a mixture of cash and BSkyB shares. However, shareholders also have the option to reject the offer .
"Many shareholders are not used to this kind of thing and are confused about their options," a spokesman for SUAM said.
The group wants BSkyB to withdraw its offer document and return any shares that have already been voted in favour of the offer.
A spokesman for the Takeover Panel said: "Clearly if people raise issues with us it's up to us to follow it up. It's something we will have to look into."
However, the panel has rejected an earlier claim by SUAM that BSkyB's offer document itself is misleading.
"The view we have taken to date is that the document is not misleading if you consider it as a whole," the panel spokesman said.
A spokesman for BSkyB dismissed the allegations. "There is nothing wrong with our offer document. It is very clear and the Takeover Panel have no problem with it," he said. "It is an offer document, so of course it talks about offering to buy shares."