The Yancoal and Glencore joint-owned Hunter Valley Operations is one of NSW's biggest coalmines, employing roughly 1500 people to dig up the fuel and send it overseas.
The company says it has contributed more than $6.9 billion to the economy, including $3.8 billion on goods and services from 750 suppliers.
Not everyone wants the Singleton mine to continue operating out to 2045, however.
Several environmental and community groups want the extension rejected to stop the greenhouse gases released on site as well as abroad when coal is burned.
They say the mine's impact on climate change is being felt locally.
"Any coal that is exported and burned outside Australia returns to us as climate pollution that fuels more dangerous disasters," Climate Councillor and climate scientist David Karoly said.
The extension proposal is sitting before the Independent Planning Commission, which is set to hear from those both in support and opposition over a series of hearings starting on Thursday.
Johnson Legal environmental lawyer Elaine Johnson said the Singleton HVO project was the first of significance before the commission since a Court of Appeal decision to overturn the approval for MACH Energy's proposed expansion of the Mount Pleasant coalmine near Muswellbrook.
The miner is now appealing that decision in the High Court, however.
Ms Johnson, who represents the group challenging the Mount Pleasant expansion, said the Court of Appeal case successfully argued the IPC needed to consider the climate impacts of the coal exported and burned overseas on the community in the Hunter Valley.
The same argument would apply to HVO North, she told AAP.
"We're not just talking about sea level rise and extreme weather events," she said.
"We're also talking about what does that mean for people who can't get housing insurance because the big insurers will no longer insure houses in flood zones."
The Mining and Energy Union Northern Mining has been among the supporters of the HVO expansion beyond 2026.
The union says it would provide a lifeline for workers at a time when several other mines are slated to shutter, and would support the local economy while state and federal reindustrialisation projects get off the ground.
HVO general manager Dave Foster said the project was a strong economic anchor for the region.
"As Australia transitions to a low carbon future, projects like this provide the stability, investment and confidence regional communities need," he said.
Groups such as the Hunter Jobs Alliance say more needs to be done to support export coalminers through an expected time of transition to stop workers being used as "bargaining chips".
The hearings also follow the NSW Net Zero Commission warning that continued coal expansions are not compatible with the state's legislated climate targets.
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