The Federal Court is expected to deliver what could be a game-changing decision on Wednesday.
The timber industry is nervously watching on amid dire warnings about what a win might mean for jobs and the economy.
The key question is whether a regional forestry agreement between the federal and NSW governments means logging activities are exempt from scrutiny under national laws designed to protect Australia's biodiversity.
The case has been brought by the North East Forest Alliance, which says the integrity of four million hectares of native forest stretching from Sydney to the Queensland border is on the line.
The North East Regional Forestry Agreement covers native forest logging across that vast expanse of coastline, which is home to endangered species including koalas, greater gliders, and the spot-tailed quoll.
It was originally inked in the year 2000 - before those species were declared endangered under federal laws - and it was renewed in 2018 for another 20 years, with rolling extensions that could continue indefinitely.
The Environmental Defenders Office is running the case and has argued the agreement was rolled over without due regard for imperilled species or climate change impacts, including fiercer fires like the Black Summer blazes that hit northern forests hard.
The forestry alliance wants the court to rule the agreement does not validly exempt native forest logging from assessment and approval requirements of the federal Environment Protection and Biodiversity Conservation Act.
"This agreement is a powerful instrument that allows the forestry industry to bypass federal biodiversity assessments," EDO chief executive David Morris says.
"Under the current system, if a population of koalas is being threatened by a new development, the project needs to be assessed at the federal level.
"But if the same population of koalas is being threatened by a logging project, it's been rubber stamped on the basis of 20-year-old environmental assessments."
The timber industry and the state-owned Forestry Corporation of NSW are keenly awaiting the outcome of the case, amid warnings of serious economic consequences if the forest alliance wins.
Australian Forest Products Association NSW chief executive James Jooste warned thousands of jobs could be on the line if there's a shutdown of logging across a large area that provides much needed hardwood for construction and other purposes.
"We're talking about one of the most critical materials and products," he told AAP.
"If there is an adverse decision ... we're calling on the Commonwealth and state governments to have an immediate plan where we don't see any prolonged stop to harvesting operations," he told AAP.
"(So) we can continue to have a sustainable hardwood industry on the northeast NSW coast."
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