Merlin Entertainments Group (MEG), which runs the attraction, filed an application in 2014 to build lodges which was rejected by the council.
The Warwick Society said the plans for glamping - or luxury camping - were not in keeping with the landscape.
MEG has previously said the site would "benefit the wider economy".
The firm applied for permission to erect up to 20 permanent lodges, and create room for 41 glamping tents on land known as "Foxes Study".
It was previously granted permission to erect a temporary site for "medieval glamorous camping".
Neighbours at the site objected to the lodges, with one saying the move would be the "first step in turning this historic heritage site into a theme park".
James Mackay, chairman of the Warwick Society, said: "Merlin is a very successful company but the proposal to use part of a Grade I listed landscape for holiday lodges is not at all satisfactory."
Warwick District Council said any public inquiry would probably be held in March.
However, it added MEG had submitted a revised application - a "scaled-down" version of the original - which would go before the planning committee in September or October.
MEG said: "Warwick Castle submitted an appeal to the decision to refuse our planning application to build new accommodation, several month ago.
"However we have also been working closely with the experts at Historic England to develop a significantly revised and reduced accommodation proposal which we hope will be approved.  If the current application is approved we will not progress with the appeal."
The owners of Warwick Castle are appealing after a council rejected plans to put a permanent "glamping" site in its grounds.