Researchers at the donor information website rated the 10 largest festivals according to their levels of charitable activity, on-site campaigning and the amount given by festival organisers.
Glastonbury, which gave £2m to charity in 2007 and this year allowed WaterAid to decorate the site's chemical toilets with African designs to mark the launch of the charity's Love Your Loo campaign, was ranked first.
But when organisers of Scottish event T in the Park heard they were going to be placed bottom and branded "big stingy losers", they took exception. They contacted Intelligent Giving and publication of the report, due today, was stopped.
A spokeswoman for the event, which has been held every year since 1994, said it had raised £600,000 for local causes, was carbon-neutral and encouraged schemes such as a tent-recycling initiative, in which discarded tents are donated to charities.
"You won't find any details on our website or press coverage about this because we believe that it should not be about PR but actually about giving something back to our community and partners," she said.
She said the report had been "incredibly poorly researched" and defamed the event's character.
A spokeswoman for Intelligent Giving said it would apologise. Initial research had been gathered from websites and secondary sources, and there would now be deeper research before the report was released.