A mining company has again been stifled in its attempt to proceed with a new open cut coal mine in the New South Wales Hunter Valley, failing in its bid to overturn a court-imposed condition on the project's approval.

The NSW Land and Environment Court previously ruled that the Ashton South East Mine could only go ahead if the company, wholly owned by Chinese firm Yancoal, purchased the property of farmer Wendy Bowman.

The family of Ms Bowman, who is aged in her eighties, has been farming the land near the small village of Camberwell, north-west of Singleton, for generations.

She repeatedly said she had no intention of selling her property.

Ms Bowman has environmental concerns about the mine and said she was troubled about the loss of fertile, agricultural land.

Lawyers for Ashton Coal argued the condition was irrational and illogical and meant that any work done on the project would be illegal.

The condition was likened to a "poison pill".

But lawyers for the Hunter Environment Lobby, which was the respondent in the appeal, said the condition created certainty.

Today the Court of Appeal dismissed Ashton's appeal and ordered the company to pay the legal costs incurred by the Hunter Environment Lobby.