The Ports of Auckland is blaming striking union members for its loss of a $20 million contract with shipping giant Maersk.
But the Maritime Union says shipping companies are always playing ports off against each other to get the best deal and striking workers can't be blamed.
The company and the union have failed to agree on a new collective contract. Four days of disruption at the port ended on Monday night and more are looming.
Ports of Auckland delayed a planned mediation session with the union on Tuesday because it says the industrial action has led Maersk to move its Southern Star Service from Auckland to Tauranga.
It is about a third of the business the company has with Maersk and means the port in Auckland will lose up to 14% of its overall container business.
Ports of Auckland says Maersk has told it the possibility of further industrial unrest is central to the decision.
It says it has already warned the union that strike action during one of the busiest times for shipping could cost it a major customer and threaten jobs.
Given the magnitude of the loss, it has decided to postpone mediation until later in the week.
Union president Gary Parsloe says the company escalated the dispute by locking out union members.
Maersk says its weekly Southern Star service will call at Tauranga instead of Auckland and it does not expect a material change in transit times for exporters and importers.
The company's Northern Star service will continue to call at Auckland.
Maersk says most of its export cargo currently shipped out of Auckland come from Waikato and Bay of Plenty.
It says imports destined for Auckland usually end up at the major distribution hubs in south Auckland, which are served by Port of Tauranga's inland MetroPort.
Maersk says the industrial dispute at Ports of Auckland played a part in its decision, because customers want certainty their goods will be delivered on time.