The RSPCA could be seen as being "too political" and risks losing its best staff, according to a leaked memo from its deputy chair.
Paul Draycott wrote a six-page memo for his fellow trustees in August in which he set out the biggest challenges faced by the charity.
The memo has been posted onto the internet by James Barrington, an animal welfare blogger and former executive director of the League Against Cruel Sports.
Draycott wrote that a lack of staff development and a pay freeze at the RSPCA over the past five years could lead to an exodus of the charity’s best people, leading to a situation where "we end up with a rump of those who cannot get a job elsewhere".
He also said that a lack of strategy at the top is like leading the charity into the "charge of the Light Brigade".
He wrote that a "more vocal" stance on campaigning activity by the RSPCA over the past 18 months had not been accompanied by a strategy to manage its increased visibility, likening it to the ill-fated cavalry charge.
Draycott said the charity had been trying to reverse a financial decline for five years but he understood that the charity would post a deficit of about £3m in 2013.
Attempts were being made to improve the charity’s finances by appointing a commercial director to develop new income streams in partnership with pet food and insurance brands, he said.
But he said these ideas were under threat because of the potential risk that the RSPCA could be seen as "too political", making other brands nervous of associating with the charity.
He also questioned why the charity had failed to build an effective coalition of animal welfare charities in support of its work on prosecuting illegal hunting.
"The League Against Cruel Sports should be supporting us vocally," wrote Draycott. "Instead we appear to have fallen out with them."
But Joe Duckworth, chief executive of the League, said there had not been a falling out and told Third Sector the two charities have a "great working relationship".
Draycott referred to an ongoing campaign against the charity by the Countryside Alliance, which he said has been supported by some national newspapers, and asked: "How effective are our press office and political lobbyists?"
He added that the alliance appeared to be far more effective at damaging the charity’s reputation than the RSPCA was in return.
Draycott concluded that the charity was fighting "too many battles on too many fronts" and that it now needed to regroup and resolve its most urgent problems.
In a statement, the RSPCA said Draycott’s memo was a confidential "worst-case scenario document" designed to prompt discussion among trustees.
The charity said it was "deeply grateful" for the dedication of its staff and was looking at ways to reward them without "incurring unsustainable costs". The fundraising team was meeting its targets, the statement said.
Mike Tomlinson, chair of the RSPCA, said: "The trustees place their full support behind Gavin Grant, chief executive at the RSPCA, the management and all our people who do such outstanding work for the animals."