The extension came just days after Burke’s office confirmed to ILN that a decision would be made in early February.

It was a complete surprise to Whitehaven which was confident the thermal coal project adhered to all environmental conditions.

Whitehaven’s shares plunged more than 6% on the announcement this morning.

Maules Creek was the subject of a hoax news release last month in which environmentalists claimed the ANZ bank would be withdrawing $1.2 billion in credit for the project.

Burke has come under pressure from the Greens, environmentalists and local landholders to stop development of Maules Creek and other projects in the Gunnedah Basin which present a threat to native forests and endangered species.

"We are extremely disappointed at this further delay to this important project,” Whitehaven managing director Tony Haggarty said.

“We have spent many months working with SEWPAC [Department of Sustainability, Environment, Water, Population and Communities] and Minister Burke's office to promptly and thoroughly address any questions they have had in relation to the project, as well as providing full details of the benefits to the region.”

Haggarty said the Maules Creek approval process started in August 2010 and included extensive community and stakeholder consultation and specialist expert assessments of environmental impacts.

“A large range of stakeholders have had input into this process, including local community representatives and interest groups, local government, various NSW government departments, the NSW Planning Assessment Commission, as well as the Independent Expert Scientific Committee on Coal Seam Gas and Large Coal Mining Development and SEWPAC,” he said.

The NSW project approval was received in August last year after an exhaustive two-year process.

“Whitehaven is not aware of any substantive issues with the environmental evaluations or process which has been followed,” Haggarty said.

“We look forward to understanding the reasons for Minister Burke’s decision to extend the process and will address, as a matter of urgency, any questions or input from Minister Burke or SEWPAC.”