The body for charity chief executives, Acevo, has called for charities to be exempt from proposed changes to judicial review laws that it said could leave donors having to foot the bill for legal action by charities.
Acevo warned that the proposals, on which the government has opened a consultation, could amount to "a fundamental breach of justice" if they deterred charities from challenging government decisions.
Under existing laws, judges can choose to make companies or charities that bring judicial review cases reveal who their backers are if they think the organisation is being used as a front for another party that stands to gain.
Under the proposals, however, any charity that pursued a review and sought to cap its legal costs in advance through a protective cost order would have to disclose the names, addresses and financial details of all of their members – who could then be called on to pay the costs if the charity were to lose.
Any charity that used more than £1,500 from an individual funder to cover its legal costs would have to declare that contribution to the court – someone who had given a one-off donation to the charity that had been used to fund a case could be ordered to pay for the whole case.
Acevo member Matt Shardlow, who is also chief executive of the insect conservation charity Buglife and chair of the legal strategy group of the representative body the Wildlife and Countryside Link, said the changes posed a "very serious problem" for charities.
"It would alter the relationship between donors and the charities involved," he said. "Will donors want to give to a charity that is taking a judicial review if it could be potentially putting them at risk?"
The new requirements could also violate members’ privacy, he warned. "If you have a civil servant, for example, who is a member of a charity that is taking action against the department they work for, that could put them in a very difficult position," he said.
Shardlow said it was not known how many charities would be affected if the proposals were implemented, but the biggest impact could be dissuading charities from bringing cases in the first place.
"This is bullying and intimidating behaviour from the government, which is seeking to limit the ability of charities to hold it to account," he said.
A spokesman for Acevo said: "Judicial review is central to the rule of law, ensuring that government at all levels can be held to account for unlawful decisions.
"It would be a fundamental breach of justice to deny this right of challenge for the most vulnerable in our society."
Both Shardlow and Acevo urged charities to examine the proposed rule changes and submit their responses to the consultation, which closes on 15 September.
A Ministry of Justice spokesman said the government welcomed all submissions to its consultation.
"Judicial review is critical in making sure the government and public bodies are abiding by the law, but we also have to ensure the system is not open to abuse," he said.
"It is right that courts know who is funding applications for judicial review, especially when the claimant is arguing that they should be given costs protection.
"While delivering greater transparency, these reforms don’t affect the rules on when third parties have to pay costs."