A group of members of the National Trust for Scotland has called for the charity's chair to resign immediately and for its board of trustees to stand for re-election.
The group, called In Trust for Scotland, represents more than 2,500 members of the charity.
It has also called for a caretaker chair to be appointed to lead widespread reforms of the charity's governance, including its management systems and reporting structure, in order to make the organisation more transparent.
The move follows the announcement last week that chair Shonaig Macpherson would stand down in September 2010.
Bill Fraser, co-founder of In Trust for Scotland, called for Macpherson to stand down immediately rather than in 12 months' time.
Fraser also said the organisation needed to become more transparent.
"When we have asked to see minutes of meetings, we have been refused access to them," he said.
The group is urging members of the charity to attend its annual general meeting on 26 September to back its demands.
A spokesman for the National Trust for Scotland said the charity was looking for a new chair to replace Macpherson and declined to comment further.