The proposed Great Koala National Park aims to link dozens of koala hubs near Coffs Harbour in northern NSW to protect 100 native species, including up to one in every eight koalas living in NSW, Queensland and the ACT.
It was a major election promise for the NSW Labor government, but its eventual size is still being considered.
Several conservation organisation heads have voiced their concerns over the promised park in an open letter published on Wednesday.
World Wildlife Fund for Nature Australia chief executive Dermot O'Gorman said the promised park needed to be declared across 176,000 hectares of koala habitat.
"Not one hectare less will be enough," he said.
Greenpeace chief executive David Ritter said Australia was a global deforestation and extinction hot spot.
"The declaration of a Great Koala National Park that addresses our deforestation and extinction crises is long overdue," he said.
NSW Nature Conservation Council chief executive Jacqui Mumford said the park was the government's centrepiece environmental commitment during the 2023 election campaign.
"However it has been over 700 days and we are still waiting for them to deliver," she said.
"If they are serious about a legacy that doesn't involve koalas continuing their trajectory towards extinction, they will deliver the park in full without any further delays."
The group said ending forestry logging and declaring the park was essential to protecting an estimated 12,000 koalas.
The timber industry has preferred a proposed 37,000ha park, costing less and saving more jobs, than an otherwise acceptable 58,000ha alternative.
The government remains committed to delivering the park but has not yet decided how big it will be, Premier Chris Minns told a budget estimates hearing in February.
"We'll make a decision soon enough, but we've restricted the amount that can be land-cleared," he said.
Environment Minister Penny Sharpe told a separate hearing on Monday the government also needed to manage the impact on communities and could not provide a time frame for an announcement.Â
The government is also looking at whether it can generate Australian Carbon Credit Units through the park's creation which could be used to fund landscape restoration, Ms Sharpe told the hearing.
