NZ First leader Winston Peters would refuse to form a Government with the National Party if it increased the retirement age.
It comes after Prime Minister Bill English hinted at changes, saying it's time to reset expectations about the pension.
Mr Peters has promised the age would stay the same, at 65, and has made it one of his top bottom-lines going into any post-election deals.
"Not reneging on promises made to the retired and soon-to-retire people of this country is very important," he told Newshub.
"We intend, unlike other political parties, to keep our word and stand by the older people in the country."
Previous Prime Minister John Key had sworn to resign before raising the retirement age, but with his departure Mr English said there's a chance to "reset" expectations.
"I haven't made the same undertaking as John, so we have the opportunity for a bit of a reset there," he told The Nation.
Mr Peters isn't the only one with concerns about a changing retirement age.
With Māori life expectancy rate lower than that of the general population, the Māori Party wants Māori and Pasifika to be exempt from any increase.
One of its policies is to reduce the superannuation age to 60 for Māori and Pasifika people.