Ambulance drivers and other health workers will go on strike on Tuesday in a bitter row over savings and union recognition.
Unite said its 450 members at the Yorkshire Ambulance Service NHS Trust will walk out for 24 hours after the failure to break the deadlock.
Ambulance staff and paramedics will mount picket lines outside ambulance stations across the county.
Members of other unions are not involved in the action and will be working normally to provide emergency cover and other services.
Unite said it was derecognised after raising concerns about patient safety over plans to make savings of £46 million over the next five years. The union said there were proposals to employ emergency care assistants, with only a few weeks training, alongside paramedics.
Regional officer Terry Cunliffe accused the Trust of taking a "hardline" stance after a fruitless plea for talks over Easter to try to avert the strike. Workers launched an overtime ban last week after voting heavily in favour of industrial action.
The Yorkshire Ambulance Service NHS Trust said the action will put a strain on its 999 service but provisions have been made.
It said in a statement: "Throughout the 24-hour period of the strike, and the continuous overtime ban that Unite the Union commenced on 26 March 2013, our focus will be on taking steps to maintain operational cover to sustain effective and safe services.
"This action will undoubtedly place strain on our 999 service, and therefore the trust is reminding the public to use the service wisely for patients with serious and life-threatening conditions only during the 24-hour period of industrial action, and asks people to only call 999 for an ambulance in an emergency when it is obvious that someone has a life-threatening or serious illness or injury."
It advised anyone requiring advice or treatment for a non-emergency or minor ailment to consider self-care or visit a local pharmacist, GP surgery or walk-in centre.