Resthome operators say rural resthomes may not be able to afford new charges for non-emergency or private-hire ambulance transport.
St John Ambulance has lifted its charges by 38 percent in January for those needing non-urgent transport between their home, resthome or hospital.
The Aged Care Association says resthomes pay the cost under a contract with district health boards and many resthomes - particularly those in rural areas - will find the increased charges unaffordable.
It says it was told about the change shortly before Christmas and there was no consultation.
However, St John's operations director Michael Brooke says the organisation receives no government funding for the service and the new charges are reasonable and are needed to meet costs.
The increase does not affect the region served by Wellington Free Ambulance, whose charge for a similar service has not risen.