More than one million messages from Manchester United supporters have been sent to the club's sponsors and the banks underwriting this week's IPO to complain about the ownership of the Glazers.
The Manchester United Supporters Trust (MUST) have called for a boycott of the sponsors because half of the proceeds of the IPO, in which 10% of the shares in the club will be sold, could go to the Glazer family.
United fans are also targeting the banks supporting the flotation on the New York Stock Exchange, claiming it is bad for investors as well as supporters.
Sponsors have received over 758,000 messages and bankers a further 608,000 and Duncan Drasdo, chief executive of MUST, said: "The response has been incredible and the rate of increase shows no sign of slowing down as the campaign takes off around the world spreading like wildfire through the Manchester United global fan base.
"Manchester United fans were already angry about the £550 million the Glazers have already taken out of our club. The hundreds of millions more they plan to take in future with the proposed IPO in New York has now pushed many beyond breaking point."
An MUST spokesman added: "Essentially the IPO is bad for investors, the club and the fans. The Glazer family sell the rights to our loyalty and devotion for the club to sponsors for many millions but then use that money to pay off their self-imposed debt.
"It has to stop and we want the IPO shelved and a proper fan ownership model put in place - one share, one vote. Our actions are no different to the marketing tactics used by all the club's sponsors anyway."
The clubs' sponsors and the banks are yet to comment.