The New South Wales Land and Environment Court last month overturned the development consent received in 2012, based on an appeal initiated by the Bulga-Milbrodale Progress Association.
On Monday, the Supreme Court granted Rio subsidiary Coal & Allied’s application to expedite the appeal, with the hearing scheduled over July 30 to August 1 this year.
However, C&A managing director Darren Yeates said that while the company welcomed the decision, pressure on the mine increased each day.
"To avoid significant job losses for our workforce of 1300 people, we need access to this land right now so we can start preparing for mining,” he said.
"Even with this accelerated appeal timeframe it will be extremely difficult to maintain production levels at the mine next year, which will impact the viability of the operation.
"We are conducting a thorough review of our future options at Mount Thorley Warkworth and looking for ways to minimise job losses if we can."
The extension project would have stretched the mine life from 2021 out to 2033.
The mine has already been operating for 30 years.
Yeates said the implications for the NSW mining industry were wider.
"We'd gone through the full planning process over several years and secured approval from all the necessary state and commonwealth regulators,” he said.
"Suddenly at the end of all of this, for the first time ever, a NSW court has overturned a major project approval to extend an existing open cut mining operation.
"So we now have a new hurdle suddenly added in at the very end of the approvals project - it sends all the wrong signals to any company looking to invest in New South Wales."
Australian Coal Association chief executive Nikki Williams warned on Friday that the decision put future investment in Australia at risk, particularly if governments continued to ignore the impact of high costs, delays and uncertainties in the approval process for mining projects.
"The decision has set a dangerous precedent because it means that after a company has gone through three and a half years of extensive planning processes and finally receive government approval, the project can still be rejected," she said.
"How can any project proponent proceed with a new project if there is no end point in the planning process?
"Project proponents must have clear direction about the process that will apply to their proposal and the government requirements that have to be met. All of that has gone out the window."
Williams said Australia traded in a global coal market and it must keep its costs and its risks down, particularly at a time of difficult market conditions.
"Coal companies must have certainty in the planning process if they're to secure investment and remain globally competitive," she said.
"This is the commercial reality: uncertainty and delays cost money, and they are now costing money at a time when the Australian industry is facing pressure from low prices, high costs and a high Australian dollar.
"Governments should be ensuring certainty in regulations and keeping costs down. We cannot take the revenue from Australia's successful coal export industry for granted."
