The Engineering, Printing and Manufacturing Union has lost a three-year fight with Air Nelson over contract engineers carrying out aircraft maintenance during a strike in 2007.
The EPMU originally took the Air New Zealand subsidiary to the Employment Court, alleging it had breached a ban on strike breaking.
The Employment Court ruled that because the contract engineers carried out maintenance for the airline for a few hours each week they were not doing the work of regular staff during the strike, but their own.
The dispute went to the Court of Appeal which decided in the union's favour, saying the Employment Court had decided the case on an incorrect legal basis.
Air Nelson then appealed to the Supreme Court which on Monday decided by a majority 3-1 decision that the Employment Court was correct.
The EPMU says the case has significant implications regarding the employer's ability to employ strike-breakers during an industrial dispute.
