Yorkshire ambulance chiefs are planning to replace skilled staff with "emergency care assistants" as they struggle to find £46 million in savings because of coalition government cuts.
Yorkshire Ambulance Service NHS Trust has to find the savings over the next five years.
Unite union said the trust's proposals include the downgrading of 300 ambulance workers' jobs.
The care assistants will be expected to attend emergencies such as multiple road accidents and fires working alongside fully trained paramedics.
The union warned that the planned shake-up was "all about cost-cutting and nothing about improving patient care."
Unite regional officer Terry Cunliffe said: "Currently, paramedics undergo a two-year degree course to equip them with the correct skills to respond to patients. The new proposed emergency care assistant role will be responding to emergencies with only six weeks training.
"This could lead to situations when the emergency care assistants won't have the necessary skills to support the paramedics.
"Our biggest concern is about patient care. Members of the public will have a decreased level of clinical response with overworked staff whose morale has been badly hit by this misguided deskilling plan.
Unite has called on the trust to "have an urgent rethink of its plans."