National MPs David Carter and Nick Smith could be next to leave Parliament, a political commentator claims.
Matthew Hooton says new leader Simon Bridges is "clearing people out in the way that you would expect from someone who aggressively plans to win the next election".
Dr Jonathan Coleman was the latest to resign on Thursday, following on from Steven Joyce and Bill English stepping down.
Mr Hooton told RadioLIVE on Friday that Dr Coleman was likely pushed out because he had aspirations beyond the job he was given, claiming that Mr Bridges wanted him to lose the health portfolio.
"Quite clearly through his career his real ambition, and you have to say almost his only ambition, was to become leader of the party and Prime Minister... there's no evidence that he was passionately interested in defence or health."
At a media conference after he announced his resignation, Dr Coleman said he had not planned on resigning but received an unsolicited offer to become the chief executive of private health company Acurity Health Group.
He denied that the decision had anything to do with failed leadership ambitions.
Dr Coleman's seat will trigger a by-election in Northcote, which could cost taxpayers up to $1 million to fund, but Mr Hooton says it's just the cost we pay to be in a democracy.
"Yes it will cost to have a by-election but if he doesn't want to do the job of serving the people of Northcote at that local level for the next two and half years, the people of Northcote are better off getting someone who does."
He expects National will hold on to the Northcote seat as no Government has won a seat in a by-election in the history of New Zealand.
However it is an opportunity for Prime Minister Jacinda Ardern to "make history" if Labour could win the seat.
National leader Simon Bridges was not available for comment.