A hearing over a long running dispute between a Hunter Valley farmer and a coal company planning an expansion will begin in Sydney today.

The Land and Environment Court previously ruled Yancoal's Ashton South East open cut coal mine can only go ahead if Wendy Bowman agrees to sell her property.

Ms Bowman does not want to sell.

Yancoal will argue in court that the previous judge did not have the power to impose the condition on the project.

Ms Bowman said she is too concerned about the local environment to consider selling up.

"If something goes wrong with this permeability barrier that they want to put in between the pit and the creek, what do the people downstream of me do if they can't use that water?" she said.

Ms Bowman has been fighting against the mine expansion for years.

She argues her tiny community of Camberwell has already been decimated and need to be protected.

"It's virtually starting a new mine, for a little seven year mine," she said.

"And why? With Yancoal, their five mines are all working at a loss."