Staff at Wellington's CentrePort have been ordered to unload a ship they had blacklisted after it was loaded by non-union workers in Auckland.

The Employment Court has granted an injunction against the Maritime Union and the Rail and Maritime Transport Union.

That means both unions are prevented from stopping their members working on the Maersk Aberdeen.

The ship has spent four days sitting fully loaded in Wellington while workers went out in sympathy.

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But the Maritime Union said the workers are not doing anything unlawful because they are not actually striking.

Their lawyer said earlier what they were doing was noble and dignified, taking a stand against the way workers were being treated by Ports of Auckland.

CentrePort said in today's hearing that every day the ship sits unattended is further damaging its reputation.

But there are fears industrial unrest is spreading through New Zealand's ports.

CentrePort lawyer Michael Quigg said there has been similar action in Tauranga and it was likely to affect other ports too.

He said the situation has stemmed directly from the ongoing Ports of Auckland dispute.

The company said every day the ship sits unattended is further damaging its reputation.

Meanwhile Prime Minister John Key said the Government's watching developments but there was no intention of getting involved at this stage.

"The ports are important to New Zealand, both our reputation and also the efficient operation of our economy,'' he said.

"It would be an enormous call for the Government to get involved but for the most part ships are being unloaded, obviously the one in Wellington at the moment isn't, but for the most part the ports are still operating.''

Managers at Lyttelton Port are also keeping a close eye on the industrial unrest.

Lyttelton Port chief executive Peter Davie said he would not speculate on what may happen locally, but he was keeping in constant contact with staff and unions.