The professional body for paramedics is supporting St John Ambulance in its call for more funding to avoid increasing its callout charge.
In a letter to government agencies, which was leaked to the newspaper Herald on Sunday, St John chief executive Peter Bradley said the current $88 callout charge would have to increase.
The chair of the New Zealand branch of Paramedics Australasia, Sean Thompson, agreed that was likely if more money was not found. He also said there might have to be fewer callouts.
Mr Thompson said it was unacceptable that the country's ambulance service was run as a charity, and without increased funding, patients as well as paramedics were being put at risk.
He said it was not fair to pass the extra financial burden onto patients.
"Someone who's in a medical emergency - they're not really thinking about the financial cost.
"But when they receive a bill it's a pretty big cost to come their way when they just really need to know that they're going to receive the care they need."