Richie and Gemma McCaw are speaking out against the possible closure of the maternity ward at St George's Hospital in Christchurch.
A proposal for change has been presented by the hospital with midwives asked to provide feedback on proposed changes.
The Herald understands the changes include the closure of the birthing unit indefinitely.
A petition, started by Christchurch organisation Rata Midwives, in support of keeping the unit open had received 17,000 signatures in two days.
It's gained support from Gemma McCaw who shared a lengthy post to Instagram detailing her experience with the hospital.
"St George's Hospital holds a special place in our family's heart as we went there with both of our girls.
"I feel incredibly sad that it looks set to close as with Christchurch Women's Hospital only available for those deemed 'high risk', and Rangiora and Rolleston further away, St George's is the only primary birthing unit in the city [sic]," she said.
The past few years have already led to enormous isolation for mothers and an increasing shortage of our amazing midwives, she said.
"Please support this petition and then share it with your friends and family. Together, hopefully we can start a conversation around this and help make a difference for our Mums and babies."
Richie McCaw also shared the petition on social media. In a Facebook post, he said the decision to close would have a huge impact on Christchurch.
"Having been there with our two girls, the support and care was amazing and we can't let a facility like this shut," he said.
Although it is private, the hospital has a service contract with the Canterbury District Health Board to provide publicly funded maternity services.
St George's chief executive Blair Roxborough said they are working closely with their maternity staff who have been presented with the proposal.
"We do not want to pre-empt that process and we are seeking their feedback. We have huge respect for our maternity team and their right to be involved in this process.
"Our focus continues to be on providing information to our Maternity staff. We have extended the deadline for our staff to provide feedback on our proposal about the future of St George's Maternity Centre to April 14."
Roxburgh would not comment on specific details of the proposal.
A spokesperson for Rara Midwives said they are thrilled with the huge support from across the country.
Sheena Ross, Jackie Coursey and Candice Milner started the petition and say they have been inundated with messages from people wanting to help.
"We've had phone calls, emails and the number of signatures has been increasing steadily, especially after Gemma McCaw became involved," Ross said.
"She has personal experience of being able to make a choice when it comes to where you have your baby, and Gemma knows understands how important that is."
Ross said primary birthing services should be increasing their capacity, not reducing.
"The Burwood primary birthing unit was the most well-used primary unit in the city. When it closed in 2016, St George's was then the only one in the city and it is often over-subscribed.
"Giving birth at a primary unit or at home enhances outcomes for well-women with uncomplicated pregnancies. We are at a loss to understand why another key part of women's health services is under threat, yet again."
The Rata midwives have supported a significant number of women to have their babies at St George's, and say primary maternity units provide a vital service for communities.