Miners at Buller's Stockton open cast mine have rejected a company proposal to reduce work hours.
The mine operated by Solid Energy wants to preserve cash and reduce cost by cutting production by 20 percent.
Engineering, Printing and Manufacturing Union spokesman Ged O'Connell says the workers have been told jobs will go if they don't reduce their 12 hour shifts to 10 hour shifts.
He says it's bullying behaviour.
Ged O'Connell says the manner in which the proposal was delivered and the general deterioration in the relationship has led to the miners rejecting the proposal.