Primary schools teachers and principals strike in Civic Square, Wellington. A strike by both primary and secondary school teachers next year just became more likely.

Secondary school teachers will strike early next year after rejecting the Government's second pay offer.

The Post Primary Teachers' Association (PPTA) announced on Friday evening that most of its 17,000 members voted against the Ministry of Education's offer of a 9 per cent pay rise over three years.

Ministry deputy secretary Ellen MacGregor-Reid says it is surprised the union is "already threatening strike action next year as they still have four days of agreed bargaining on behalf of their members ahead of them before the end of the year".

PPTA president Jack Boyle said the union will call off the strike if the ministry presents a better offer before the start of the 2019 school year.

READ MORE:

* Secondary school teachers reject 'insufficient' pay offer

* Teachers unions agree to join forces in 2019 campaign

* Unions indicate a megastrike is possible next year

"Teachers do not take decisions like this lightly. We are passionate about our work and feel a responsibility to our students and their families. We have made this decision because the government has given us no other options."

Last week, PPTA and primary teachers' union the New Zealand Educational Institute (NZEI) agreed to campaign together if primary teachers and principals reject a $698 million collective contract deal. The outcome of a vote by roughly 31,000 NZEI members is due on December 4.

MONIQUE FORD/STUFF Post Primary Teachers' Association (PPTA) president Jack Boyle has called the Government's previous offer "insufficient".

PPTA members have authorised a one-day strike in term 1, 2019 regardless of NZEI members' decision.

While secondary teachers have not committed to combined industrial action with their primary counterparts, Friday's announcement means an education megastrike involving up to 48,000 teachers is more likely.

The Ministry of Education first offered annual pay rises of between 2 per cent and 3 per cent for three years – far short of the union's bid for a 15 per cent boost over one year – before revising their offer earlier this month.

ROBYN EDIE/STUFF Hundreds of PPTA members during a union meeting at Ascot Park Hotel, Invercargill on Tuesday. Teachers have voted to reject the Government's latest pay offer.

The latest offer includes a 3 per cent pay rise each year and would push the minimum salary for an untrained teacher up from $32,600 to $39,700.

It would have increased salaries for beginning bachelors-trained teachers from $51,200 to $55,948 over three years. Salaries at the top of the trained teachers' scale would have increased from $78,000 to $85,233 over the same period.

Education Minister Chris Hipkins said bargaining with PPTA was "not as advanced" as negotiations with NZEI.

"We welcome PPTA back to the negotiating table, which is scheduled to happen next week."

The Ministry of Education said it is focussed on settling negotiations and minimising disruption for students and their families.