Power line engineers in Christchurch will stop work on Friday morning over what they say is an unfair pay offer.
The engineers, employed by Connetics, are the main contractors for Orion's Canterbury power network.
The Engineering, Printing & Manufacturing Union says they want a 5% pay increase, but have been offered only 1.6%.
The EPMU says it represents 120 of the 150 engineers employed.
A rally will be held for an hour from 8.30am outside the offices of Orion Group Limited.