Authentic Resistance is co-run by Erin Hudson, who last year spoke to media on behalf of Warnings About Vaccination Expectations (Waves) NZ, which had paid for an anti-vaccination sign by the Southern Motorway near Middlemore Hospital.
The Authentic Resistance event is being hosted as health officials warn parents of unvaccinated children to not take them in or out of Auckland as authorities try to contain a worsening measles outbreak that has reached more than 800 confirmed cases.
Immunisation is the best protection against measles and the MMR vaccine is available free from GPs.
Starship Children's Hospital head Dr Mike Shepherd has warned some children are likely to die because of the outbreak, saying "we have a highly effective and extremely safe vaccine which prevents this infection - the vaccine means measles can and should be eradicated from our shores".
Authentic Resistance has been approached for comment.
Brenda Hinton, director of a company that runs the maternity centre, told the Herald that Authentic Resistance was independent of Mama. She didn't agree they were promoting anti-vaccination messaging.
"I've got no comment to make other than we are just renting them space."
According to the Authentic Resistance website, Hudson is not anti-vaccination but "believes that parents must keep the right to decide whether to vaccinate their families or not and it should be based on information from the medical literature available. To vaccinate for the 'greater good' in her opinion is not a good enough reason".
Luise Brandt, one of the self-employed midwives who rents rooms in Mama Maternity, said the planned event didn't concern her.
Brandt "absolutely" supported people choosing to vaccinate their babies.
"There are over 20 of us midwives who work there, and I don't know if any of us don't support vaccination."
A Herald analysis of immunisation data from every neighbourhood in New Zealand has found just 77 per cent of 6-month-olds are now getting their vaccines on time, down 4.5 percentage points since rates peaked in 2016. Coverage of at least 90 per cent is needed for herd immunity.
The drop has been most marked for Māori babies, falling 9.5 percentage points to 61 per cent vaccinated; and for babies living in deprivation, down 7 percentage points to 69 per cent.
Around a quarter of the total decrease can be accounted for by parents who declined vaccines, meaning the rest were going un-immunised for other reasons such as access to healthcare.
Vaccination - the facts
• Vaccines are extremely safe, with side-effects very rare and normally nothing more than a sore arm. Licensing of a vaccine needs exhaustive evaluation and testing and every batch is controlled separately.
• There's no problem giving several vaccines at a time. A child is exposed to many more antigens from a common cold than they are from vaccines.
• Vaccine-preventable diseases are serious and can cause complications including pneumonia, blindness, infection and death. This suffering can be prevented with vaccines.
Source: World Health Organisation (WHO)