He said it was one of the few promises Mr Peters could keep if he put up a members bill. "For the record I don't support legalisation of marijuana and won't be putting up a bill for it; or promising it and then unpromising it 5 minutes later," Mr Osborne said.
Mr Peters said he did not personally support legalising cannabis and had never smoked it himself.
It was NZ First's longstanding policy for citizens' initiatied referendums to be enforceable.
Mr Peters also said Labour should pull down all its candidate Willow Jean Prime's hoardings in the Northland byelection to help his chances of winning.
Mr Peters has consistently denied he had asked Labour to ratchet back its campaign or entered any deal with the party. Yesterday he said it would be a shame if he was defeated by a small margin because Labour kept some votes.
He said he was not calling on her to do that but "if I was a rational, sane person making that judgement in the interests of Northland, I'd pull my signs down.
It's over to her. I'm not asking for anything, I'm asking her to put her people here first rather than some hopeless cause." Ms Prime's response was a blunt "no."
3 News also reported Labour had ditched a $20,000 mailout of pamphlets urging candidates to vote for its candidate Willow Jean Prime, despite fundraising for it.
Instead it did a smaller scale mailout - and leader Andrew Little has offered to refund the donations of those who wanted it.
Mr Peters said the pamphlet would have been a waste of money because many Labour people already realised it was a two-way race between himself and National's Mark Osborne.