Maritime Union members will now take full strike action for two weeks against Ports of Auckland.
A one-week strike is due to start on 24 February and a further one-week strike starting on 2 March has now been added to that.
It will be the longest industrial action by the union's members since they first walked off the job in November.
Union president Garry Parsloe says the company will not negotiate over the terms of a new collective contract.
A partial strike that began on Wednesday will continue until Wednesday next week.