Union spokesperson Joe Gallagher said the mill's last day would be December 18, and at least 72 workers at the mill had been affected.
Oji Fibre Solutions said it was considering closing the mill, partly due to high power prices, and up to 75 workers would be affected.
Earlier this month, 230 workers at Winston Pulp International were told the sawmill and pulp mills near Ruapehu were both closing for good.
About 30 workers attended a meeting at the Auckland milll this morning.
Work at the site was paused for 24 hours.
The company's announcement pack given to workers, which RNZ has seen, said this was to give staff time to go home, digest the news, and talk to their families and loved ones.
It said it had no choice but to cease operations at the mill after suffering a three-year pattern of losses.
"We see no prospect of the situation improving, and we cannot continue the way we are now.
"We've looked at every lever we could pull. We've considered a very thorough submission put forward by your unions and the questions raised by individual employees.
"But at the end of the day, there's nothing we could find that would make enough of a difference."
The company said the mill had a skilled workforce and leadership team, and the closure decision wasn't to do with them. It would be offering CV advice and interview technique workshops to staff.
Labour leader Chris Hipkins called on the government to do more about electricity prices following the confirmation of closure.
"I think this is a sign of market failure and something the government should get on top of very quickly," he told Morning Report.
Ahead of the meeting, Gallagher told Morning Report workers were resigned to being told there was a closure.
He said a combination of factors was behind the current situation, including power and gas prices, but also a lack of past capital investment.
Gallagher said $50 million in capital upgrades was needed if the mill were to remain open.
"They ruled that out as a solution.
"I think the signal is quite clear that the announcement today will be a closure.
"We've got to support these workers and it's a pretty tough time, leading up to Christmas, to lose your job," Gallagher said.
