Yorkshire Ambulance workers are to be balloted from March 6 with a strike.
Following the ballot, the strike could follow on March 25.
Unite is concerned by the trust's decision to introduce emergency care assistants (ECAs) to work alongside trained paramedics.
The ECA staff are given six weeks' training, compared with a paramedic's two-year degree course.
The introduction of ECAs forms part of plans by the trust to save £46m over the next five years.
The trust has previously decided to "de-recognise" Unite.