Settling the teachers' pay dispute could cost around an extra $135 million a year - almost as much, over four years, as a new Poseidon aircraft.

The Ministry of Education and both teacher unions have declined to provide costings of the remaining union claims, citing an agreement not to talk before a meeting with Education Minister Chris Hipkins tomorrow aimed at resolving the dispute.

The NZ Educational Institute (NZEI) said: "Ahead of Thursday's forum with the Minister we've agreed we won't be making any public statements."

NZEI's original claims included a 16 per cent pay rise