A decision on whether to grant permission for a multimillion pound potash mine on the North York Moors National Park could have implications for other national parks.
York Potash hopes to place the mine in Sneaton, just outside Whitby.
However, campaigners say that the area must remain protected.
Supporters are arguing that the decision will bring 4,000 new jobs to the area and massive economic benefits.
The planning decision was due to take place last Monday but has been deferred for a third time to allow the company to assess the environmental impact.
The final decision may now not be made until next year.