In the face of such pressure, it is likely a matter of when not if the age increases.
Meanwhile, other parties who oppose the policy do so for less optimistic reasons than National.
Mana and the Maori Party say it is unfair on those groups, such as Maori whose life expectancy is lower than the norm and who therefore won't enjoy as long a taxpayer-funded retirement as others. The Maori Party wants a lower entitlement age for some New Zealanders "to allow more equitable uptake of New Zealand superannuation for all citizens".
The Greens oppose it because it is unfair to those unable to work beyond 65. However, co-leader Russel Norman has indicated Labour's proposal for a "transitional payment" largely addresses their concern.
The case for making KiwiSaver compulsory is less clear cut. New Zealand undeniably has a savings shortage.
Australia is often held up as an example of how compulsory savings can generate a large pool of investment funds that boost economic performance, but the research on this is not unanimously positive.
National's policy for "soft compulsion" via auto-enrolment addresses concerns that a compulsory scheme would put an additional squeeze on the low paid by preserving the right to opt out.
Both major parties acknowledge compulsion and soft compulsion would impact on wages as employers offset their higher contribution obligations under both policies when negotiating pay increases.
Labour's compulsory KiwiSaver policy is far more costly than National's auto enrolment at $1.9 billion over five years compared to $550 million over four years but Labour's would result in a larger pool of savings.
National argues that as the funding for Labour's savings policy will come from debt, it does little for overall savings. That is also its argument against Labour's policy to resume contributions to the NZ Super Fund before the Government's books return to surplus.