Lyttelton Port workers have gone on strike after failed pay and safety negotiations yesterday.
Around 200 members of the Rail and Maritime Transport Union are involved in the action, which could last another 13 days.
"No ships will be able to berth, no maintenance will be done, a lot of the container terminal will stop working," RTMU organiser John Kerr told 1 NEWS.
The Christchurch Port Authority says the RTMU refused a salary increase of three per cent for each of the next three years, an offer it described as "generous".
Mr Kerr said that was "pretty inflammatory" given that members of another union were offered more, although the Maritime Union members had also agreed to controversial roster changes as part of the deal.
RTMU members are also in dispute over docked pay after they withdrew from notified protest action last week.
They have formed "peaceful" picket lines outside the port today and say they remain open to negotiations with the port company.