A move by the Lyttelton Port to stop a planned strike has failed, the Rail and Maritime Transport Union (RMTU) says.

Photo: SUPPLIED

Two hundred RMTU workers - about half of the port's staff - were planning to go on strike from this Thursday over failed pay and safety negotiations.

A Lyttelton Port Company (LPC) spokesperson said the company challenged the validity of the strike notices and applied for an interim injunction in court over the weekend.

However, RMTU's spokesperson, John Kerr, said the court overturned the application.

"Lyttelton Port Company's application ... has failed," he said.

"We've currently issued 14 strike notices as of today, we have mediation for tomorrow but if that is not successful in resolving things then industrial action can commence from Thursday."

Tomorrow's mediation would be the 23rd meeting between the RMTU and the LPC.

Mr Kerr said the 200 workers all came from strategic areas, including marine and mechanical maintenance.

"If they are all out on strike the port will have to close," he said.

Mr Kerr said the main issue the union was concerned about was safety.

"The company wants to introduce changes to the hours of work and from our perspective that will demonstratively increase the risk of fatigue, and in an environment like the port that could be a killer."

He said it was now possible for employees to work for 16 hours in a day.

"When you are dealing with straddle and cranes, that is not a good thing."

The Lyttelton Port Company had previously said that RMTU's salary increase demands were "unreasonable and unacceptable".

However, Mr Kerr said that was "complete rubbish".

"All we are asking for is a nominal wage increase of 4 percent, a 12 month term, and to get around the table to talk about safety and fatigue," he said.

LPC operations manager Paul Monk said it was disappointed that a planned strike was going ahead.

"We are offering RMTU members at least a 3 percent salary increase a year for three years and the changes we are seeking are not substantial," he said.

"LPC's offer is comparable to our settlement last year with the 201 members of the Maritime Union of New Zealand (MUNZ), the other major union at our port."

Mr Monk said there had been no safety or fatigue issues reported from staff already working on the changed roster system.

"The roster LPC has proposed to RMTU has been safely and efficiently worked for the last year by MUNZ members at the port and they have experienced no fatigue issues associated with it.

Mr Monk said the strike would have a serious impact on port operations.

"Their strikes will cause significant disruption to our customers and if they proceed with the industrial action for more than a week, as they are threatening to do, then shortages of some critical supplies will begin to occur which will affect the region," he said.

RNZ asked the LPC what those critical supplies were, but they would not specify where there would be shortages.

"We are working with our customers to determine where the risk areas are and what options exist for managing these," Mr Monk said.