Stead Foundation members are calling on the government to stop the National Trust of Australia (NSW) from evicting the current tenants at Wirrimbirra Sanctuary.
The tennants, the David G. Stead Memorial Wildlife Research Foundation of Australia, were forced to relocate their native friends after receiving an eviction notice last month.
Stead Foundation members Margaret Kitson and her daughter Janine said the eviction "threatened both the existence of the Stead Foundation and Wirrimbirra itself".
"Without the Stead Foundation, Wirrimbirra Sanctuary ceases to exist, as the foundation owns the trading name 'Wirrimbirra Sanctuary'," she said.
"The eviction may even destroy Wirrimbirra Sanctuary's State Heritage Statement of Significance for its 'role in the development of the conservation movement in NSW; its association with key persons who pioneered the conservation debate'.
"The Stead Foundation and Wirrimbirra are intertwined memorials to two of Australia's greatest environmental pioneers David G. Stead (1877-1957), and Thistle Y. Harris Stead (1902-1990)."
The Stead Foundation's relationship with the National Trust has been strained for many years.
Janine Kitson, a former National Trust Director, said the foundation was one of the National Trust (NSW)'s most significant donors
"It was the Stead Foundation who gifted the land at Wirrimbirra Sanctuary to the National Trust in 1965," she said.
"They did this on the understanding that the Stead Foundation would manage, finance and build Wirrimbirra Sanctuary.
"And indeed, since 1965 the Stead Foundation have managed, fundraised for Wirrimbirra buildings, accommodation huts, visitors centre, native nursery, library as well as dams, gardens and memorials.
"The National Trust holds bequests of nearly $400,000 for Wirrimbirra Sanctuary with no indication of what will happen to them when the Stead Foundation is evicted from the property.
"Nor is there any transparency on who will take over the management of the property."
A National Trust spokeswoman said the $400,000 bequest funds, known as the Dew Sisters Bequest may be used for the 'conduct of the Barbara Dew House', which incorporates the Field Studies Centre located at the property.
"It is very understandable that members of the Stead Foundation are passionate about ensuring the long term future of [the property]," she said.
"The National Trust's primary concern has been the protection of this significant place and ensuring its long term sustainability."
The sanctuary, along Remembrance Drive, has existed since 1962 as an education and conservation facility.
The National Trust has found a new operator for the sanctuary.
However the spokeswoman said the preferred candidate for the lease of the property would not be announced until mid-October.
"The National Trust and the successful candidate are highly cognisant of the heritage value of the property and the environmental significance of the place," she said.
"This has been an important criteria for the board of the National Trust during the assessment of submissions made during the Expression of Interest process, and in the board's final decision on the successful candidate."