It is a historic first - with primary and secondary teachers taking to the picket lines together in a move which has the potential to affect every state-run school in the country.
The Ministry of Education is seeking an urgent return to talks to avoid the strike. But the Government has indicated it will not budge on a $1.2 billion offer previously offered to teachers.
Teachers unions say the offer doesn't go far enough and fails to address teachers' towering workloads and the need for extra resources.
Fifty-thousand members across the primary teachers' NZ Educational Institute (NZEI) and the Post-Primary Teachers' Association (PPTA) will take part in the strike.
If it goes ahead - on the eve of the Government's much-vaunted May 30 "Wellbeing Budget" - some parents may be forced to take the day off work to look after their children, others may have to negotiate working from home or bringing their kids to the office.
Others will be scrambling for babysitters or asking grandparents or other relatives to take the kids.
For some parents struggling to find care options, schools may be able to open their doors - but only if they have teachers who are non-union members.
Michael Williams, president of Secondary Principals' Association and principal of Pakuranga College, said how schools respond to the strike action would very much vary from school to school.
"You'll see different ones, from schools where everyone's a union member and so there will be no one on site so there will be no kids on site, through to, in the secondary sense there will be people who will still be at school," he said.
Secondary school principals will not be on strike, as their contract does not fall under the current negotiations.
"Other schools may have some non-union members who won't be on strike and so they have to be at work, therefore some schools will offer a service to their parents if the parents can't look after the kids the school will step in and do that," he said.
"Conceivably a school could run a part of the school with non-union staff members, [but] I don't know if anyone's going to be doing that or has the resources to do it, or the willingness.
"I think to a large extent secondary principals are very supportive of their teachers needing to have their salary and workload addressed."
Williams said he will be at school on strike day, and expected there to be some non-union members in his school who would also be at work.
"It's very likely that at Pakuranga [College] we will have some staff who are non-union members and we'll use them to supervise. So we'll offer to our parents if they can't arrange care for their kids then we will supervise the students in the library."
Teachers were aware not all parents have the capacity to miss a day of work and schools "will do what we can", he said.
He added: "I think we've seen right across that the public is generally very supportive, they realise that teachers are not getting a good deal, despite what the minister is trying to tell everyone."
Parents would have to talk to their children's schools in order to find out whether it will be closed completely on May 29, or partially open for those who are unable to miss a work day.
An upshot of both primary and secondary schools striking at the same time would be older teenagers being able to look after younger siblings or babysit for neighbours, Williams said.
"It will help to some extent having secondary schools off at the same time," Williams said. "There will be lots of secondary students babysitting siblings, neighbours' kids etc. so that should really help out with the young kids."
The New Zealand Educational Institute (NZEI) said teachers were willing to lose a day's pay in order to "send a strong message to the Government that they can't wait another three years until the next round of negotiations to fix the crisis in our schools".
"Your child's school will advise you shortly about whether the school is completely closed on May 29 or if there will be some limited supervision available for families unable to make alternative arrangements," she said.
"There will be rallies and meetings around the country on May 29. Everyone who supports the teachers is invited to attend. Details of events will be released soon at
"Teachers hugely appreciate the support that parents have expressed so far. They're asking anyone who supports their campaign to consider phoning or emailing your local MP to let them know you back the teachers – regardless of whether your MP is in Government or Opposition."
The Ministry of Education said schools were encouraged to remain open for instruction during the strike action if it had non-union member teachers.
"For some schools it may not be possible to safely provide supervision sue to the availability of staffing, in that case parents and carers will need to make other arrangements."
It added: We know that strike action is disruptive for you and your children, and will continue to make every effort we can to settle the collective agreements with the two unions."
The New Zealand School Trustees Association is expected to publish advice for school boards later today.
The teachers' strike will come five days after a second national student strike for more action on climate change, scheduled for May 24.
It is the third time primary teachers will take to the picket line in a year, but the first time in New Zealand history that primary and secondary school teachers have voted for a combined all-schools strike.
Strike facts
When: Wednesday, May 29, 2019.
What: Primary and secondary school teachers to take part in the first all-schools combined strike.
Who: State and integrated schools nationwide. Almost 800,000 students to be impacted.