Two of New Zealand First's former MPs, Tracey Martin and Jenny Marcroft, have left the party.
Martin has long been involved with New Zealand First, along with her mother and former party president Anne Martin.
She served as a minister in the coalition government and was an MP from 2011 to last year, when New Zealand First failed to return to Parliament.
But Martin said New Zealand First was no longer the party she had been closely involved with for the past decade and she had no choice but to quit.
"There were policies that were announced during the election campaign that were a surprise to me, there were situations where I believed I understood what New Zealand First stood for over the last two to three years and found myself up against a different perspective inside my caucus and that was very difficult," Martin said.
"But also the structure of the party that I was part of, particularly between 2008 and 2011, was very democratic, it was very membership based. It was a team and the changes that have been made inside the party over the last couple of years have become much more executive-led and less democratic."
New Zealand First's campaign pledge to lower the tobacco excise so that the average pack of cigarettes cost no more than $20 was an "interesting" policy and "just came out of the blue", she said.
There were other policies that had been worked on "quite strongly" that were never announced, Martin said.
Martin hasn't spoken to New Zealand First leader Winston Peters, who she has long had a close relationship with, about her resignation and said "why would I?"
"I'm a grown woman with my own ability to make decisions on my own and ... I don't require either Winston's permission or Winston's approval."
When asked about her long relationship with Peters, Martin said it was always in a "work environment."
"I admire Winston Peters on many, many levels but I didn't need to let him know or check this with him. The process for me to resign from this political party was to let the president know and I did that at a face-to-face meeting and wished them well," Martin said.
Marcroft said she had been considering her future with the party since the start of the new year and tendered her resignation on Monday.
Her primary reason for quitting was for future job opportunities, she said, but the party's culture was another factor.
"As the only two women in our caucus, we were very aware of the difficulties that there were for women in a party like New Zealand First," she said.
"For me, I would need to see a greater gender balance. I'm interested in working with people that embrace women."
Marcoft was concerned about a shift in the party which she had noticed in the last Parliamentary term.
"I wasn't really comfortable with that shift," she said.
Marcroft said she would "potentially" return to politics "if there is the right opportunity, if the party aligns with my own personal values, then I would definitely want to consider that and so I'm not ruling anything out at this stage".
Acting President Darroch Ball declined a request by RNZ for an interview, saying he had no comment to make.