The Engineering, Printing & Manufacturing Union says a recent proposal by an aircraft engine overhaul and repair company will result in more skilled workers leaving New Zealand.
The Christchurch Engine Centre, co-owned by Air New Zealand and Pratt & Whitney, plans to close one of its working lines which could result in up to 40 job losses.
The JT8D line handles mainly older engines on Air New Zealand Boeing 737 and 727 jets.
EPMU spokesperson for aviation, Strachan Crang, says unless more specialised lines are created in New Zealand, workers will have to look overseas.
"These are really highly specialised roles. So we'd need a new line to be developed or some more work to be developed around aircraft engines in New Zealand or else it is very likely that these guys will go into the global market for aircraft engineers and gas turbine engineering.
"It's sad to see these guys - a lot of them will face moving offshore to get work in their specialised field."
Mr Crang says the engine line became unprofitable because of the high New Zealand dollar and a reduction in clients.