Workers at Lyttelton Port Company will resume strike action at midnight tonight after employment talks failed to reach an agreement today.
Strike action forced the port to close last week before negotiations began again, but no agreement was reached.
The Rail and Maritime Transport Union (RTMU) has said the two key sticking points were the port company's refusal to pay staff who returned to work after an earlier strike notice was lifted, and its refusal to give parity with another port union
But the port company said the RTMU did not want parity with the Maritime Union of New Zealand (MUNZ) - the other major union at the port - it wanted an unfair advantage over it.
The company said RMTU members wanted the same salary increase their colleagues received, but without making the roster changes MUNZ accepted a year ago.
It said the port wanted to stop the enormous disruption the RMTU strikes would have on shipping lines, importers and exporters.