Lyttelton Port workers could strike for up to three weeks – potentially closing the vital trade link – after a vote to endorse industrial action.

The Rail and Maritime Transport Union (RMTU) balloted its membership on Thursday, presenting two courses of action after a failed mediation meeting with the port on Tuesday.

The meeting was the 21st sit-down between Lyttelton Port of Christchurch (LPC) and the union to negotiate a new collective contract covering about 200 waterfront staff.

SUPPLIED Rail and Maritime Transport Union members at a meeting where they voted to back industrial action at Lyttelton Port of Christchurch.

RMTU South Island organiser John Kerr said there was unanimous support for both a ban on overtime, or a complete withdrawal of labour for up to three weeks.

READ MORE:

* Mediation fails to resolve contract dispute at Lyttelton Port

* 'Significant disruptions' ahead as Lyttleton Port strikes continue

* 'Families matter' to striking workers unhappy with rostering at Lyttelton Port

The union now had a "mandate" to proceed with industrial action. It planned to go back to the port, and depending on the response "we'll either be around the table talking, or issue a notice of action".

"We don't want to agree to something the company is proposing which we don't think is safe, and which in our view they're not paying enough for," Kerr said.

LPC chief executive Peter Davie said the port had made RMTU members a generous offer of annual salary increases of at least 3 per cent to accept what he described as "small changes".

However, he claimed the union was asking for increases of up to 15.45 per cent for some members, on top of "substantial increases" over the past three years.

"These are well paid jobs," Davie said.

"It sounds like Marie Antoinette saying the peasants can eat cake," Kerr said in response.

"This is a guy whose being paid $1 million a year, and we're arguing over shekels."

Davie was Christchurch's highest paid public boss last year, taking home $955,000 – a point of contention for many union members who view it as "exorbitant".

The port last year reached an agreement with the other major union, the Maritime Union of New Zealand, for a "more efficient roster alignment" in the container terminal, Davie said.

He said he was keen to see the arrangements adopted by RMTU members, adding a roster had been agreed upon but "we reject their unrealistic wage demand".

"We are a fair and reasonable employer but such salary demands by RMTU are unreasonable." He said he was hopeful "we can continue to make progress and reach agreement".

Kerr said the union had no problem with the port changing people's hours of work so it could operate 24/7, but it needed to be done safely and there seemed to be a a reluctance to adequately compensate workers.

The port was "offering nothing" to cargo handlers unless they shifted to hours Kerr believed were unsafe, while maintenance workers would have their earning power "compromised" under the new roster.

"These changes will impact people's ability to spend time with their families and earn a decent living."

The union was required to give 14 days' notice for any industrial action. Kerr said if it came to a full withdrawal of labour "the port will shut – no questions about that".

"But that's the last thing we want to happen. We would much rather get this sorted out around the table. But I'm very, very clear that our members are resolute."