Midwives worry pregnant women could be left in lurch if maternity carers can't work because of the vaccination mandate.
The government says all high risk health workers must be fully vaccinated by 1 December - that also includes nurses, GPs, pharmacists and paramedics.
The College of Midwives backed vaccinations and said the vast majority of its members did too.
But chief executive Alison Eddy said the workforce was so stretched that if any refused, it could mean there was not enough maternity cover at the busiest time of the year in December.
"The nature of the workforce issue for maternity are such that we just can't afford to lose any midwives," she said.
The December deadline was too soon, she said.
A later one would give the district health boards and other midwives time to plan care, and the college more time to persuade any reluctant members, she said.
Eddy did not know exact numbers who were vaccinated, but said most were.
The College has traditionally taken a stance of encouragement rather than mandating vaccinations, but understood why the government has made the decision, she said.
With more time, they might be able to persuade any reluctant people rather than losing them from the workforce, she said.
NZNO industrial services manager Glenda Alexander said they were also considering what to do with anyone who would not - or could not - get vaccinated.
She hoped most would be able to be redeployed to non-frontline jobs rather than not being able to work at all.
Most nurses supported vaccinations, seeing first hand why they were needed, and compulsory shots were nothing new to those who had been in the profession awhile.
"Years ago, we didn't even think about it, there were quite a lot of mandatory vaccinations required before you could even start your training," she said.
There was wide support from GP groups for the measures.
The Pharmacy Guild said it was still getting its head around the fresh news before working out how it would affect its members.
Epidemiologist Michael Baker said he was pleased to see the mandate but said it needed to also include non-medical staff - like cleaners.
"We basically have to mandate for all workers who enter the premise of any healthcare institution in New Zealand now," he said.
He also wanted rapid antigen testing of all hospital visitors.
The latest DHB figures, from last month, showed nearly 90 percent of staff across Auckland were fully vaccinated, with much lower rates in some other DHBs.
The DHBs said they were complying the latest rates this week and were confident there was high coverage.
RNZ
