A small division of Contact Energy will begin an indefinite strike on Friday.
Up to 10 drivers who work for Rockgas, a branch of Contact that delivers gas cylinders, have been involved in an industrial dispute for the past two months.
First Union, which represents them, says the drivers earn $2 an hour less than their competitors and have limited rights when hurt.
Spokesperson Jared Abbot said Contact is refusing to listen to the drivers and the only option left is to strike.
Mr Abbot said this could problems for customers and suggested that they stock up in case the strike lasts for a long period.
Contact Energy is confident its customers would not be affected by the strike and said more negotiations are scheduled for next week.