Labour leader Jacinda Ardern is poised to make a major education announcement that will be a flagship promise in her campaign.

Labour is set to announce its biggest spending pledge of the campaign on Tuesday, when it is expected to promise a big boost to its existing tertiary education policy.

The announcement at an Auckland college will coincide with its own "opening of the books" as it reveals its updated fiscal plan that takes into account Treasury's updated forecasts revealed last week.

Free education has been a repeated theme in leader Jacinda Ardern's speeches, sparking speculation she will unveil a fast-tracked version of the party's "three free years fee free" tertiary promise.

Dasha Kuprienko Former Labour leader Andrew Little announced Labour's first stab at a tertiary policy in 2016.

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That policy, unveiled by former leader Andrew Little in his "state of the nation" speech in early 2016, promised three years free education for tertiary students and other "post-school" education.

Under Little's policy the three years, free of course fees, could be taken at any time across a person's life.

The policy would have applied to university students, apprenticeships or for training or retraining in NZQA approved purses.

Labour has costed it at $265 million in the first year rising to $1.2 billion at full implementation.

But that would not have been until 2025, prompting speculation Labour would bring that forward to make a big campaign impact.

The 2016 pledge would have applied only to undergraduate study and would be phased in starting in 2019 with one year, two years from 2022 and three years from 2025. It would not apply to those who have already undertaken post-school study.

Under Labour's fiscal plan, prior to Tuesday's update, the party was planning to spend $417 million in 2018/19 on education, but that is set to rise significantly.