Ports of Auckland workers began a 24-hour strike on Tuesday night, despite a fourth pay offer from the company.
About 300 employees downed tools about 11pm on Tuesday, and were due to discuss on Wednesday whether to accept the latest offer.
The company is offering a 4% increase in the first year, and an additional 3.1% to offset the removal of some allowances.
The offer also includes a 4.5% rise in the second year, and 4% in the third.
Ports of Auckland managing director Jens Madsen said the timing of the industrial action could not be any worse, as it is close to Christmas, and the country is suffering an economic slowdown.
He said the strike was unneccesary and irresponsible.
Port management says four vessels will be affected by the action.
Maritime Union president Denis Carlisle said the workers did not plan to go on strike at the port's busiest time of year.
He said union members were frustrated at the lack of progress in reaching settlement with the port company.
Importers Institute secretary Daniel Silva said importers are worried that continued industrial action could affect retailers in the lead up to Christmas.
