Greenpeace says it is stunned Genesis Energy is considering restarting a mothballed coal-burning unit at Huntly Power Station.
Chief executive Marc England told industry publication Energy News that a coal-burning unit currently in storage at the site "could be re-commissioned if the market made it desirable".
A Genesis spokesman confirmed to Newshub the move is a "long-term option on the table".
Greenpeace NZ senior campaign advisor Steve Abel says it would be a backwards step that would amount to "climate change denialism".
"This is the company who were proposing to shut the Huntly Power Station a couple of years ago and now under England they are proposing to expand their use of the dirtiest fuel on the planet."
Huntly operates four units burning gas and coal, with two others currently in storage.
Genesis Energy announced last year that it would shut down the units at the end of 2018.
However, in April it announced the plants will operate until December 2022.
Genesis has defended is approach to coal, saying coal-fuelled generation at Huntly was down 37 percent in the 12 months to the end of June 2016.