The Salvation Army hopes discounted sanitary products being sold at a supermarket chain will increase the number of donations to women who need them.
Countdown is selling a range of pads and tampons for $4 for the next fortnight, to encourage consumers to buy some for women who cannot afford them.
The two organisations launched a joint campaign last year, along with Labour MP Louisa Wall, to highlight the financial struggle women faced in order to take care of their menstrual health.
Salvation Army territorial social services secretary Pam Waugh said the families she worked with had tight budgets and often had to go without sanitary products.
"Some families can be spending up to $25-30 [per month] if they've got two daughters and a mum," she said.
"We don't want people having to make choices between whether you can have a basic essential need such as a sanitary pad, or do you have food."
The Salvation Army had already received $25,000 worth of sanitary products since the campaign began last year, Ms Waugh said.
She hoped the latest initiative would increase the donations so the charity could distribute them to women most in need.
Small supermarkets were also doing their bit.
Parakai Four Square owner Daniel Dale said his west Auckland store would be donating one sanitary product to the Helensville Women and Family Centre for every one bought in his store for two weeks, starting 17 April, as well.
"It is an issue that's carried on, it's not something that's popped up once and disappeared," he said.
"So being in the trade where I sell those items, I thought there's definitely something we can do to help out there."
Mr Dale had talked to other supermarket owners, who were interested in carrying out a similar initiative, he said.