More than 1,000 people have signed a petition calling for a site picked out by Center Parcs for a holiday village to be protected.
If planning permission is given by Mid Sussex District Council, a 553-acre swathe of Oldhouse Warren, in Worth Forest, could become home to a £350-400m village made up of 900 lodges.
Launched by Sarah Gore-Booth, the petition on change.org states: "Whilst we have nothing against a new leisure facility in the South East, this is clearly the wrong location.
"This is irreplaceable habitat with a unique ecosystem of soil organisms, fungi, invertebrates, birds and mammals that have evolved together over centuries, even millennia.
"It must be protected and ideally restored to its full potential."
It was a view shared by Crawley councillors, who have agreed that leader Michael Jones should write to both Center Parcs and the district council, laying out their concerns.
Naturalist and campaigner Dave Bangs, of Protect Oldhouse Warren, said allowing the holiday village to be built would 'rip the heart out of Worth Forest and destroy the integrity of the largest block of ancient woodland in the middle of the Wealden Vale'.
Instead, he supported the idea of a re-wilding and forest-wide restoration in line with the likes of Ashdown Forest, the New Forest and Epping Forest.
Mr Bangs added: "A Center Parc would reduce the naturalness of Oldhouse Warren to 'wallpaper' - a cosmetic background marketing a lucrative quasi-urban holiday enterprise.
"This cannot be allowed to happen.
"Worth Forest is worth saving."
Responding to concerns raised, a Center Parcs spokesman said the company took its responsibility to the environment and forests 'extremely seriously'.
Detailed ecological surveys would be carried out to inform the designs and construction environmental management plan for the site.
They added: "We have more than 30 years' experience of sensitively managing the woodlands in which our villages are located, carefully nurturing and maintaining the forests to protect and enhance biodiversity.
"Our approach to this development will be a collaborative one, working with the local authority, local community and with all groups that have a specific interest in the site."