Marama Fox says Countdown reducing the prices of its sanitary products is a step away from the days when women had to use rags or moss while on their periods.
The supermarket has announced it will make its Homebrand and Select menstrual products more affordable to combat what's known as the 'period tax' - an additional expense women have to pay because of their biology.
Guest hosting RadioLIVE's Drive show on Tuesday, the Māori Party leader commended Countdown on the move, but her co-host Ryan Bridge was less convinced.
He said he accepts that because of his poor eyesight he has to spend money on glasses and contact lenses, an expense other people don't have to pay for, and asked why women having to pay for sanitary products are any different.
Ms Fox says the consequences for women who can't afford sanitary products are unhygienic and humiliating.
"How would you feel that you've got a blood flow falling out of your vagina that you cannot stop? When you can't afford a pad or a tampon, what have you got at your disposal? A wad of toilet paper? Rags ripped up from towels that you then wash out and use again and again?
"Back in the day my aunties tell me they used to get moss off trees and use that. Literally this is what we're asking women to do if they can't afford sanitary items."
She says it's unfair that free condoms are available from schools, nightclubs and Family Planning clinics, but tampons aren't free for women who need them "by no choice of their own, except gender".
Menstruation is a symbol of women's ability to grow life inside them, which Ms Fox says should be respected and provided for.
"But for us you wouldn't be here, so let's do something to ensure these women are able to be supported because we cannot have people who are impoverished literally walking around with wads of toilet paper stuck between their legs all day."
Watch the video for the full conversation.