Auckland trains will run at reduced services from this weekend, as rail workers take industrial action.
There may be cancellations, and peak-time train services will run at a reduced 20-minute frequency from Saturday, operator Auckland One Rail said.
Negotiations for a new collective agreement had reached an impasse, Rail and Maritime Transport Union general secretary Todd Valster said.
"We've been bargaining with [Auckland One Rail] for the last eight months - it expired about eight months ago, and we've been working away trying to reach a compromise, and there's been a couple of major issues that we haven't been able to get past."
Valster said rail workers were refusing to work overtime or work changes to rostered hours.
Disputes included removing a clause guaranteeing train drivers the majority of their weekends off, and what Valster described as a lack of trust to resolve workload issues for three major work groups.
"The company want to resolve them during the term of the agreement, and there is absolutely no trust that that will occur."
The relationship had deteriorated, Valster said.
"This is definitely not what good looks like. The last time I put in strike notices for collective negotiations was well over 20 years ago, so I know how relationships can be built up, and there is a fairly poor relationship between the Rail and Maritime Transport Union and Auckland One Rail."
Auckland One Rail chief executive Martin Kearney said AOR had been working hard to avoid industrial action.
"We're disappointed that, while we felt we were near agreement, negotiations have broken down and resulted in the current notice of industrial action which we know will have an impact on our customers," he said in a statement.
Train crew worked shifts on a 24/7 roster and AOR acknowledged the impact shift work could have on people's lives and as a result paid well above the median wage as a result, Kearney said.
AOR's latest offer was a 6.1 percent increase to pay rates and allowances for all roles covered by the collective employment agreement for an 18-month term, he said. Kerney said AOR had also provided some assurances around weekend work.
He said AOR had written to the Rail and Maritime Transport Union asking that any industrial action was postponed so further talks could take place.
Auckland One Rail and the union would go into mediation next week to reach a resolution.
But if disputes were not resolved, Valster said the action could continue for a month.
In a statement, Auckland Transport rail franchise manager Craig Inger said it was disappointed it got to this point.
"We understand how deeply frustrating this will be for our rail customers, who have already had to endure ongoing disruption while we work with our partners to prepare the rail network for the opening of the City Rail Link," he said.
"We understand [Auckland One Rail] and the union will be meeting for mediation next week in order to obtain a timely resolution. We encourage both parties to meet and continue bargaining in order to prevent ongoing disruption to Aucklanders."
Auckland Transport said trains for Saturday's Blues vs Fijian Drua game at Eden Park would still be operating.