Politicians have called for a watchdog investigation into whether the "staggering" £326,000 spent by the RSPCA on legal action against a fox hunt was a breach of the charity's obligations.
Tory MP Simon Hart, the former head of the Countryside Alliance, has written to the Charity Commission along with a small cross-party group of MPs and peers asking it to investigate.
The commission said that "on face value" there was no reason for it to intervene however, and that it was a matter for the animal protection charity's trustees to scrutinise the spending.
Last Monday the Heythrop Hunt – with which Prime Minister David Cameron has ridden in the past – admitted four charges of intentionally hunting a fox with dogs on land in the Cotswolds, in breach of the ban.
District Judge Tim Pattinson imposed a £4,000 fine on the hunt and smaller fines on two individual members and told it to pay £15,000 towards the RSPCA's costs.
But passing sentence, he also said he found "quite staggering" the sum spent by the charity bringing the prosecution.
"Members of the public may feel that RSPCA funds can be more usefully employed," he said.
The politicians, including Labour's Kate Hoey, Liberal Democrat Mark Williams and Tory former Cabinet minister Lord Heseltine, raised concerns in a letter to commission chairman William Shawcross.
"We believe that this 'staggering' expenditure constitutes a clear breach of the 'duty of prudence' by the trustees of the RSPCA in that it cannot possibly be argued that charitable funds and assets have been used reasonably," they said.
The prosecution could have been brought more cheaply using in-house lawyers, they suggested.
"Instead, hundreds of thousands of pounds donated to the RSPCA by members of the public have been squandered unnecessarily."
The duty of prudence is not a legal requirement under the charities Act 2006 or other legislation.
A commission spokeswoman said: "At face value there's nothing we can see for us to take forward."
It said trustees had to act "in accordance with the charity's aims and powers, and acting prudently".
"Undertaking such prosecutions is in furtherance of the RSPCA's charitable objects and is made clear to the public on their website. It is for trustees to consider the matter of bringing prosecutions in accordance with these duties and any other requirements which might apply, and for them to consider the issue of costs."
A spokeswoman for the RSPCA said its trustees had "acted entirely within the society's charitable objectives and procedures and charity law."