Winston Peters has called Prime Minister John Key's bluff by refusing to rule out going with Labour because of its plans to raise the pension age, saying changes wouldn't kick in during the next term.

"Realistically, it's not an issue," the New Zealand First leader said.

Labour wants to raise the age of eligibility for super from 65 to 67 between 2020 and 2032. NZ First's policy is to retain the current age of 65.

Key has said the age will not rise while he is prime minister, but he's becoming increasingly isolated after economists, the retirement commissioner and other political parties agreed the cost of the scheme had to be addressed.

Key, who last week said he was "holding hands with Winston" over the issue, yesterday laid down the gauntlet to Peters.

"I dare him to go out there and say he will not under any conditions form a government with Labour, even if Labour's policy is to raise the super age from 2020, not in the three-year period from 2014 to 2017.

"I dare him to say he will not, because he's tricky and he'll find a way all around all of that stuff."

But Peters took exception. "Tricky am I? I never worked for a company that took the American people to the cleaners and then went broke and got the American people to bail them out," he said, referring to Key's time with investment company Merrill Lynch.

He said NZ First would not do a deal with another party 2 1/2 years out from the next election, and the challenge showed National was in trouble.

Key was "running out of friends, support and excuses", Peters said.

Peters also hit back at Key's comments on the infamous teapot tape – that NZ First's supporters were dying off – saying they knew they couldn't trust Key any more than previous National leaders who had lifted the age of entitlement and raised the surcharge rate.

"This is about people's lives, not some sort of tawdry deal in the dealers' room."

While super wasn't a deal-breaker next election, he said asset sales were. "Everybody knows it's a bottom line. We walked out over the sale of Wellington airport, and we would not go down that road again."

NZ First is holding its annual conference in Palmerston North this weekend and Peters will give his keynote speech today.

He is expected to call for targeted immigration, raising concerns low-skilled migrants are not matching the "quality" of the New Zealanders moving to Australia.

- © Fairfax NZ News