Burke’s office had earlier told ILN that a decision on Maules Creek and an extension to Idemitsu’s Boggabri mine was due in early February. But last week it was unexpectedly delayed, sending Whitehaven Coal’s shares down more than 6%.

A spokesman for the Department of Environment said: “Final decisions under national environment law on the Maules Creek and Boggabri mining proposals in New South Wales have been extended until 30 April.

“Subject to negotiations with the companies, the minister could make the decisions sooner.

“The timelines were extended by a delegate of the Environment Minister to seek clarification on potential impacts to matters of national environmental significance.

“Given that the Maules Creek and Boggabri projects are proposed to be located very close together, it is appropriate that their respective impacts are assessed in parallel, to look at their cumulative impacts as a whole, and to ensure they deliver long-term environmental sustainability for the region.”

Burke is under pressure to make an interim decision on Boggabri and Maules Creek, but is threatening to cut the NSW government out of the approvals process in a replay of his clash with Queensland’s Campbell Newman government over approval for the $6.4 billion GVK Hancock Alpha coal project in April.

Burke is locked in a dispute with NSW Minister for Resources Chris Hartcher, who accused him of delaying the project because it could be damaging ahead of this year’s federal election.

"A serious question mark hangs over the federal government's planning process in relation to economic development,” Hartcher told The Australian.

"The federal minister has been shown to be prepared to manipulate the process for what can only be described as a blatant political purpose - to achieve the re-election of the Gillard government.

“The federal government faces a serious challenge to its economic credentials and this will only weaken their credentials further. There is almost a billion dollars of investment involved here, meaning hundreds of jobs and economic growth for the region and the state, yet none of this seems significant to Tony Burke."

Burke told The Australian: “"I accept the NSW government is angry with me at the moment over coal-seam gas, but to think that this gives them a licence to release commercially sensitive information is a deeply irresponsible path.

"The only way I can deal with that is to cut NSW out of deliberations."