Wharfies at Wellington's Centreport are supporting their northern counterparts by refusing to unload a ship recently arrived from Auckland.
The Maersk Aberdeen arrived in Wellington on Friday but workers there refused to handle its cargo as it had previously been unloaded in Auckland by non-unionised workers.
About 300 Ports of Auckland wharfies are on a three-week strike, which looks likely to extend, over the company's moves to casualise their work.
Centreport staff picketed over the Maersk Aberdeen on Friday, Saturday and again today, and Centreport management has sought an Employment Court injunction to force them to unload it.
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"We're acting reasonably and responsibly to resolve a situation that's not of our own making, while respecting the rights of customers and staff, and maintaining our business," Centreport chief executive Blair O' Keeffe said.
"There are no health and safety issues, or employment negotiations involved in the dispute.
"Staff are legally obliged to fulfil the conditions of their collective employment agreement, and we hope that they will do that."
The Employment Court was scheduled to hear the case tomorrow.
Maritime Union of New Zealand general secretary Joe Fleetwood said the union and Centreport were in talks and it was possible the problem could be resolved before it got to court.
"It'd like to say yes but, then again, it may be no," he told APNZ.