"A low production volume has made reinvestment in the ageing plant not viable."
A final decision on the sawmill's future would be announced next Wednesday, following consultation with employees and the union, it said.
The company's processing site in Ngongotaha, where 20 staff are employed, would continue to operate while other options were considered.
Mamaku Residents and Ratepayers Group secretary John Rush said rumours of the mill's closure had been circulating for a while.
"I think everyone was pretty clued-up about it, but no one really, really expected it to happen. All of the workers come from Rotorua so a lot of good Rotorua people will be losing their jobs."
He said the closure would have a ripple effect on local business.
"The sad thing is when they close that sort of thing other businesses feel it," he said. "The garage probably, and the store where they buy their lunches, but other than that it won't have a big effect on the town.
"This mill is going to be the tenth mill in the country that's gone 'phut'. It's a big worry to us all. We've got the timber now with the dairy industry having low payout, and sawn timber mills closing all over the country - what's next? These could be tough times."