Deputy Prime Minister Winston Peters says NZ First turned down a proposal from Advance New Zealand to join forces.
"Advance New Zealand wanted to join New Zealand First but we said no," Peters said.
He was speaking in Tauranga's Red Square and responding to a woman holding a poster with images of Prime Minister Jacinda Ardern and communist symbols.
Asked why the party refused, Peters said the reasons would be "obvious to any sensible, sane, rational person".
"Advance New Zealand came and tried to join," Peters said. "We said no."