Nearly 200 union members working at Lyttelton Port won't get paid for four days when 11 members go on strike in two weeks.
The Rail and Maritime Transport Union and the port company have been in a month-long dispute over pay and rosters.
Eleven staff who operate the boats that take pilots out to incoming ships will strike from 26 April.
Lyttelton Port chief executive Peter Davie said none of the union's 191 members would be paid for the strike days because, without pilots, ships couldn't get into port.
"Legally it is termed a lockout yes, we gave them notice saying that if your union is shutting the port by using these 11 staff members that the rest of them, we won't have work for them over that period and we won't be paying them.
"We've offered a very fair pay settlement - if you got offered 3 percent, I think most people in New Zealand would take it," Mr Davie said.
A union spokesperson, John Kerr, said he hoped the dispute could be resolved before the strike began.
