Three New South Wales coal mines have been given federal government approval to extend their operations for the next 30 to 40 years.

The mine extensions are expected to secure the jobs of more than 1,800 mine workers in the Hunter Valley and Narrabri regions, according to the government, but have angered environmentalists and the Greens who have accused the government of "gaslighting" voters on its emission reduction targets.

The approvals are for MACH Energy's Mount Pleasant Optimisation project and the Ashton Coal Operations' Ravensworth Underground Mine, both near Muswellbrook, and the Narrabri Underground Mine Stage 3 Extension Project owned by Whitehaven Coal.

A spokesperson for Environment Minister Tanya Plibersek said in a statement to the ABC that the government was considering the mines on a case-by-case basis under the law.

"The Albanese government has to make decisions in accordance with the facts and the national environment law — that's what happens on every project, and that's what's happened here," they said.

"The emissions from these projects will be considered by the minister for climate change and energy under the government's strong climate laws that were supported by the Greens political party and independents."

The climate law they refer to is the "safeguard mechanism", which sets legislated targets, known as baselines, on the net greenhouse gas emissions for facilities that emit more than 100,000 tonnes of carbon dioxide in a year.

The mechanism only covers emissions generated in the process of digging the coal out of the ground and does not consider the emissions generated by the coal when it is eventually burned.

The Greens' environment spokeswoman, senator Sarah Hanson-Young, said Labor's environmental credentials were in tatters.

"This goes to show the Albanese government has zero credibility on the environment this election after approving three coal mine extensions in a single day," she said.

With government approval, MACH Energy will be able to deepen part of the existing Mount Pleasant mine, build a road and extend the life of the mine.

Earlier this year a group of concerned community members failed to overturn the NSW Independent Planning Commission's approval of the Muswellbrook mine.

The approval notice for the Ashton coal mine said it would "conduct underground longwall mining of coal seams at the Ravensworth Mine Complex, develop associated infrastructure and transfer coal, water and gas to the Ashton Coal Project, in Ravensworth".

Whitehaven Coal will also now be allowed to extend its existing underground mine at Narrabri, with limits on clearance in areas of habitat for listed threatened species.

Environmental group Lock the Gate Alliance spokeswoman Carmel Flint said she was shocked the minister chose to issue the approvals so close to an environmental conference.

"Minister Plibersek is holding a so-called 'Global Nature Positive' conference in just two weeks in Sydney, but she's sent nature into a devastating negative spiral with these three approvals," she said.

The Australia Institute think tank also called the decision "shocking", while Australian Conservation Foundation spokesperson Gavan McFadzean condemned the federal government for approving the mines while trying to take action on climate change.

"This decision is the opposite of climate action," he said.

"Together, these coal mines will generate more than 1.3 billion tonnes of lifetime emissions which will undermine Australia reaching net zero by 2050."

But Minerals Council of Australia chief executive Tania Constable said the approvals would safeguard jobs and economic stability in a region that relied on the industry.

"These projects have faced lengthy delays due to appeals exploiting legal loopholes in our environmental laws, driven by third parties disconnected from the needs of local communities," she said. 

"While the courts ultimately dismissed these claims, it hasn’t come without a cost to the taxpayer and local communities."

A landmark climate case brought by the Environment Council of Central Queensland in the Federal Court last year found Ms Plibersek was not obliged to consider the climate harm of new coal and gas projects.

The case referred directly to the Narrabri and Mount Pleasant mines.