The NSW ambulance service is struggling to send two paramedics on each call-out, exposing lone responders to violent attacks, the union says, arguing 1000 new staff are needed to address the "crisis".
The warning from the Health Services Union comes after the NSW government announced it would not support a recommendation from a lower house inquiry to "eliminate the need" for single-officer responses.
"This is all about paramedics being assaulted," HSU NSW secretary Gerard Hayes told AAP on Monday.
NSW has about 4000 operational paramedics, according to the union, and that's not enough to always have paired crews.
"How do you cover this state with those numbers?" Mr Hayes said.
Last year's parliamentary inquiry into violence against emergency personnel recommended the government "explore resourcing options" to eliminate single-crew responses and boost paramedic numbers in regional NSW specifically.
Many of the inquiry's recommendations have already been accepted but Health Minister Brad Hazzard last week said "more consideration was needed" when it came to lone responders.
The government argues single-crews have reduced response times and are routinely supported by other emergency services.
The union will sit down with Mr Hazzard on Friday to urge the government to hire 1000 new paramedics.
Almost a third of those would service the rapidly expanding population in Sydney's west.
"This is a crisis that will affect paramedic safety and their ability to deliver advanced clinical outcomes to their community," Mr Hayes said.
The complexity of treating patients makes it difficult for lone operators to get the best outcome, he added, but many paramedics are forced to take calls alone.
"Generally they go out because there's just no one else."
Alcohol, the increasing use of drugs like ice, and the stress caused by any emergency, means paramedics are often "soft targets" for abuse, Mr Hayes said.
NSW Ambulance and Mr Hazzard have been contacted for comment.