Lyttelton Port has been threatened with six days of strike action from 11 February by the Rail and Maritime Union.
Talks with workers ended last week with what the Rail and Maritime Union described as "only a slight improvement" on the port company's original pay offer.
It's offered workers an increase of 3 per cent over 18 months, backdated to September.
The port said it had received strike notices for three consecutive days from the union and had been told it will be served with three more.
Chief executive Peter Davie said because of the length of the strike, the port would only be able to provide some services.
Mr Davie said customers will need to plan ahead.