Primary and secondary teachers may unite against the government next year if their pay disputes are not settled.
The teachers' unions have confirmed their leaders are meeting at the end of this week to discuss a combined campaign.
It's not yet clear if both groups of teachers will decide to keep fighting.
Members of the Post Primary Teachers Association are still voting on whether they should take action over their collective agreement, while those in the NZEI will vote in a couple of weeks on the latest offer they have received from the Education Ministry.
However, the two unions say their executives have scheduled a meeting on Friday to discuss a joint campaign in 2019.
"Both unions are facing the same fundamental problem - a government that is refusing to invest adequately in teachers and principals to address the huge challenges that the sector faces," a PPTA spokesperson said.
"We'll be looking at the development of joint campaign plans to be put into action in 2019 to support member activism and community engagement."
The Education Minister, Chris Hipkins, has urged the Educational Institute to calm tensions around the primary teachers' pay talks.
The union today began a week of one-day rolling strikes in primary and intermediate schools despite being told by the Employment Relations Authority last week that its demands were unrealistic.
Mr Hipkins said the government tried to avoid the strikes and it wanted to continue negotiation.
The government will not add more money to the offer, which is worth nearly $700million over four years, he said.