A group of retired Southland coal miners says Solid Energy has reneged on a deal which guaranteed them discounted coal for the rest of their lives.
The miners are entitled to a supply of high-quality coal for use on their ranges, but have instead been offered lower-grade lignite which they say is not up to scratch.
They signed a collective agreement entitling those with at least 20 years service to up to 10 tonnes of cheap coal a year once they retired.
But the Engineering, Printing & Manufacturing Union says the offer was withdrawn and lignite offered instead, when the Ohai mine closed last year.
Southland organiser Trevor Hobbs says lignite is vastly inferior because it produces less heat and more smoke and ash.
Mr Hobbs says the miners were also offered one-off cash payments or alternative home heating devices worth up to $4500, but the value was worth much less than the coal.
Solid Energy says it has made an offer which more than meets its obligations under the miners' collective agreement.
The state-owned enterprise says the deal has been accepted by about two-thirds of the miners.