National Party leader Simon Bridges says Kris Faafoi's position as a Cabinet minister is "untenable", if it's proved he helped a friend's relative with their immigration case.
Newshub on Thursday revealed a series of text and Facebook messages between Faafoi and rock singer Jason Kerrison, of Opshop fame, in which Kerrison asks Faafoi for help with his step-father's declined partnership visa application.
Faafoi tells him he'll "talk to the people that can speed things up" but "can't put anything in writing", but soon cuts off communication.
Faafoi told Newshub he'd stopped replying to Kerrison's messages "because it wouldn't be appropriate", but National says by then he'd already gone too far.
"If what's alleged is proven correct, I think Kris Faafoi's position is untenable," Bridges told Newshub.
"Cabinet ministers must uphold the highest ethical standards at all times, and this is the opposite. In a Government I lead, if proven, he would be gone."
National MP Paul Goldsmith told The AM Show on Friday Bridges would show no mercy.
"If it was me under a National Prime Minister, I'd be toast. You'd be spreading your peanut butter on me right now.
"When you're talking about messages saying, 'Look, I've got a plan, keep it quiet, let's not talk about it, I'll do my best', and acknowledging there's a conflict there, it doesn't look very good."
He said Prime Minister Jacinda Ardern "never disciplines anybody", pointing to New Zealand First MP and Cabinet minister Shane Jones' repeated indiscretions.
Labour's Willie Jackson defended Faafoi, but admitted the situation was "messy".
"I think we'll be able to work our way through it because the reality is he didn't make any decisions in terms of what was happening here. The thing with Kris is he's a good man, he's not just a good minister. He's a great community man."
Jackson said Goldsmith's comments were typical National.
"There's no second chances with National - cut everyone's throat, lock everyone up, throw the key away. Punitive, punitive, punitive. Goldie would kill ol' Fafs off. It's not right."
Ardern wasn't aware of the messages between Faafoi and Kerrison until being contacted by Newshub.
Bridges himself has been accused of corrupt and unethical behaviour by former National MP Jami-Lee Ross, whose allegations sparked a Serious Fraud Office investigation into the party's finances which is ongoing. Bridges has denied any wrongdoing.
Former MP Maurice Williamson resigned his ministerial portfolio in 2014 after phoning police to inquire about an investigation they were conducting into a National Party donor.