Judith Collins says she deleted her 'woman of colour' tweet after a staff member told her it was offensive.
All the sponsoring MPs are women of colour - Jo Hayes, Priyanca Radhakrishnan, Jenny Marcroft and Golriz Ghahraman.
"MPs band together for female genital mutilation ban," Collins tweeted. "I am a woman of colour - the colour white - and I fully support a ban on this mutilation inflicted on women."
The tweet was met with outrage on the social media site.
"All Judith Collins needed to say was that she is opposed to female genital mutilation without injecting any form of white supremacy into it," said @jamesalcrow.
"Judith Collins saying she is a woman of colour (white) is the whitest thing I've ever heard in all my days," joked comedian Brendan Kelly.
Collins said she was "trying to show solidarity" but admits she messed up.
"I wasn't trying to offend anybody," she told The AM Show on Friday. "I was trying to be empathetic and you know, even I - just occasionally - can make an error. Only very, very occasionally."
One of her staffers convinced her to take it down.
"I came back to the office and a staff member said to me, 'that's insulting' and I said, 'why?' And she told me why she felt it was, and I thought, 'It's not worth a battle. Just delete it.'"
She still insisted 'white' is a colour.
"Many people would think so."
Labour MP Willie Jackson, appearing with Collins on The AM Show, defended his rival against accusations of racism - but not her "stupid" tweet.
"Judith obviously is not a woman of colour, but she is a woman of some substance, alright? We get sensitive about everything. I do understand why some of our people would be.
"Judith was actually supporting women of colour, but women of colour are women who are right at the bottom of the heap, that's what they're saying. They've been racially discriminated against, they haven't had an opportunity. Some might get upset, but Judith has proven herself with a lot of Māori women out in Papakura and they know that she supports them.
"Judith's a bit like Shane Jones - they can be incredibly brilliant, and now and then, stupid. That was an example of it."
Collins wasn't done provoking Twitter's left-leaning crowd however, later tweeting: "I was asked what is the opposite of 'woke'? I suggested 'Awake'. Thoughts?"