Prices for runners packages for the 2005 Great North Run have risen by 50 per cent since last year. Charities are now being charged £3,750 for 75 runners' places, compared with £2,500 last year.
Charities claim that the hike in prices was implemented without proper consultation.
"We are naturally concerned that, without prior discussion, the cost of the charity package was suddenly and significantly increased," said Craig Fordham, chairman of the events managers' forum, which represents charity events teams.
"In the future, charities cannot be relied upon to fund similar increases."
But Nova International, which organises the race, said participating charities should think of themselves as "investors" in the future success of the race.
"An event like this isn't cheap to run, and charities raise significant amounts of money through it," said Nigel Gough, events director at Nova International. "We're asking charities to invest with us and improve the quality and standard of the race for participants."
He said that the money from the price increases would go towards a new website, a partnership with BT, more marketing to promote the event and facilities such as big screens at the finishing line.
The RSPCA says that it is being priced out of the race. "We understand that there is a supply and demand rationale behind these increases," said a spokesman. "However, if prices continue to rise we would have to consider whether it would be better to target runners with ballot places rather than booking guaranteed places."
Large charities such as the RNID and Macmillan Cancer Relief say that the price hikes will have a considerable impact on how much they will raise from the event.