Voters are almost equally split over Labour's plan to lift the age of entitlement for New Zealand Superannuation from 65 to 67, according to the latest Herald DigiPoll survey.

Just over 48 per cent of those polled disapproved of the idea against just under 47 per cent who approved. Around 5 per cent did not express a view or refused to say.

Although there was firmer backing for compulsory saving for super, the poll finding suggests the policy might not be quite the game-changer Labour was hoping.

Of some relief to Labour is that nearly 60 per cent of those saying they would vote for the party approved of raising the age over Labour's intended time-scale of 12 years from 2020.

However, that still leaves one-third of the party's support disapproving of the policy change. There is clearly some disquiet among core Labour voters with a policy that will especially have an impact on workers engaged in arduous jobs.

There was also resistance among those aged 18 to 39 - a population segment many experts thought was resigned to seeing the age of entitlement for the state-funded pension rise. Just over 50 per cent of voters in that age group disapproved, against 45 per cent who approved.

A slightly smaller majority of those aged 40-64 also disapproved, while a reasonably clear majority of those who are 65 or older approved of raising the age. That age group would not be affected by the phasing-in of the hike in the qualifying age.

Despite John Key's opposition to the proposal, nearly 40 per cent of National voters expressed approval.

Labour is on stronger ground with its accompanying promise to make KiwiSaver compulsory for all workers and lift the employer contribution to 7 per cent by 2022.

Just short of 58 per cent approve, while nearly 36 per cent disapprove.