The Maritime Union is warning of an exodus of workers from Ports of Auckland if the company restructures its workforce.
The port company wants to make workers redundant and re-employ them through private contracting firms.
The union met company representatives on Friday and said the discussions confirmed that 330 workers face redundancy.
Union president Garry Parsloe estimates that nearly a third of those workers would not re-sign with a contractor if restructuring proceeds.
About 40 older workers may take their redundancy payment and retire, about the same number may head to Australian ports and others will look for alternative work in New Zealand.
The union says some workers are in line for redundancy payments of $80,000.
Ports of Auckland says it's confident the best performing staff will be highly sought after by the new contractors.