A group of protesters are planning to chain themselves around an old beech tree to try and save it from being cut down.
The tree is on land planned for development in Trebanos, near Pontardawe.
Neath Port Talbot Council says the tree is dangerous due to a root infection but residents living nearby are horrified it is being felled.
Leah Hopkins said: "It's really upsetting. They're saying it's diseased but I think there should be the chance for a second opinion. We understand that only recently it was regarded as being in a healthy and safe condition.
"My family have been walking around there for the last 10 years and we always go and see that tree. It's the granddad of trees, it's huge.
"What's happened now is someone has come and slashed all around the tree, girdling it. It's just so sad. The site is huge and you would think the trees would be an asset to the developer."
It is understood the tree is hundreds of years old and is being cut down on Monday.
In 2015, the site at Trebanos House, The Drive, gained planning permission for the demolition of an existing care home and the construction of a replacement two-storey residential care home for six adults.
But in 2017 new plans were put forward to the council for pre-application advice for 12 homes on the site.
Ward councillor Rebeca Phillips said she had been in contact with council officers and hoped the tree could be saved.
She said: "This situation demonstrates how important it is to make sure any trees of significance are protected. I hope that concerned residents' voices are heard by the authority and the site developer."
A Neath Port Talbot council spokesman said the tree was not covered by any Tree Preservation Order (TPO) and could be felled without requiring permission.
He said: "Officers are aware of the tree in question, and have previously inspected the tree at the request of the landowner.
"This inspection identified that the beech tree has a substantial area of root infection and under tree inspection criteria is classed as dangerous and high risk.
"Accordingly, while the tree contributes to local amenity, it has been concluded that it would not be appropriate to support a TPO in view of the report on the health of the tree."
Applicant Michael Forzani of the Care Management Group has been approached for comment.
