Ports of Auckland has issued a second lockout notice to union members who are threatening to strike.
More than 300 members of the Maritime Union are planning two strikes of two days each, one from Thursday and another starting on 8 December.
Ports of Auckland says its intends to lock them out for two days after each strike.
Chief executive Tony Gibson says the parties have reached an impasse, but if the union withdraws the industrial action notice he will lift the lockout.
He says the company is offering a generous deal with a fair pay rise of 2.5% and other incentives.
However, union president Garry Parsloe says Ports of Auckland is giving staff who are not in the union more money and union members can not accept that.
He says the last lockout at the port was in 1951.
The Manufacturers and Exporters Association says the lockout will have major repercussions for businesses.
Chief executive John Walley says the advance warning of the lockout has meant some ships can be re-routed, which has reduced some, but not all, of the costs to businesses.
"There'll be a cost of delay, there will be a cost of loss to reputation, people don't like to think that things are easily disrupted," he says.
Mediation between the port and the union will resume on Monday.
