Manchester United fans opposed to the takeover of their club by Malcolm Glazer yesterday urged sponsor Vodafone to "hang up" on the billionaire businessman.
Protesters at the mobile giant's annual meeting claimed Vodafone was at risk of being associated with a " severely tainted brand".
They said Vodafone's public image would suffer if Mr Glazer's leadership of the football club proved unsuccessful.
Oliver Houston, vice-chairman of Manchester United Supporters' Trust, said Vodafone could suffer enormous damage by sponsoring the club.
He said: "If Manchester United does fail financially, as many think it will, it will be the biggest failure football or sport has ever seen. Vodafone will be tied in with that."
He said nobody was pretending fans were going to cripple Vodafone financially but its public image could suffer greatly.
"We are here to make a clear message that we are not going to go away," he said. "This could be a very, very big issue for Vodafone."
Opponents to Mr Glazer's takeover of the club earlier this year have vowed to boycott Manchester United merchandise in a bid to devalue the brand. They have also said they will stop people buying anything related to the sponsorship of the club.
Fans have protested at the amount of debt included in the takeover, which requires £540 million of borrowing, including a £265 million loan facility secured against United's assets.
Mr Glazer's plans for the club are said to include raising its revenues by 52 per cent by 2010.
Protesters held up posters saying "Hang up on Malcolm Glazer" as shareholders made their way into the meeting.
A number of investors put the issue to the board inside the AGM.
Prof Jonathan Michie, a small shareholder, said sponsorship of the club was a very serious matter for Vodafone.
He said: "I know subscribers will switch in the future if the board does continue with sponsorship of Manchester United."
He urged the board to reconsider its sponsorship, adding: "It could only do Vodafone damage."
His words were met with applause from the rest of the packed meeting room.
Chairman Lord MacLaurin said the board had been associated with Manchester United for some time.
"We have a contract with them," he said. "We will review that contract as and when."
Another investor, James Masters, asked about the impact on subscription numbers.
Head of marketing Peter Bamford said the number of cancellations in protest at Manchester United was "very very small".
He said the number was tiny compared with the benefits brought to the business and that he saw no reason why it could not continue to be of benefit.