The union which represents ambulance workers in Yorkshire says plans to change shifts could affect patient safety.
Workers across the county walked out at midnight for a 24 hour strike.
Yorkshire Ambulance Service NHS Trust refutes the claims made by Unite.
Our members, who are doing their best for the Yorkshire public in very difficult circumstances, have been under sustained attack by the trust's hardline management for more than a year.
The latest erosion in their employment conditions is the demand to work elongated shifts, which could mean them working more than 10 hours on the trot before managers deign to give them a meal break. This could affect their ability to do their jobs - helping people in distress.
I think the people of Yorkshire will find that this is completely unacceptable.
The chief executive of the Yorkshire Ambulance Service NHS Trust said the industrial action would affect services, involving around 8% of its staff.
He refuted claims by the workers' union, Unite, that changes in shift patterns would affect patient safety.
I would like to reiterate that I remain deeply concerned over this type of action - which I know is of concern to all of our A&E staff, who are very committed to patient care - and will place many of them in a very difficult situation.
Our focus is on safeguarding patient care, and we are committed to minimising the level of disruption to our services.
Industrial action in this form is certainly not in the best interests of patients, and it is deeply concerning for a trade union representing ambulance service workers to strike without making any concessions to patient safety.
– Yorkshire Ambulance Service NHS Trust chief executive David Whiting
Mr Whiting added the service will take steps to 'maintain operational cover' during the strikes, and will 'continue to make every effort to get to patients as quickly as possible whilst maintaining high standards of patient care.'
Five hundred ambulance workers have joined picket lines across Yorkshire and North Lincolnshire for a 12 hour walk out.
Members of the Unite Union are taking action because they say the Yorkshire Ambulance Service NHS Trust are risking patient safety, by allowing new emergency care assistants to work with paramedics after only six weeks training.
Over the next five years the trust has to cut their budget by forty six million pounds. They say they'd like to reassure the public that the level of disruption will be minimal during industrial action.
Our members are increasingly concerned about patient safety because of the downgrading of the current skill level on NHS frontline vehicles in Yorkshire. We call yet again on the blinkered, hardline management at the Yorkshire Ambulance Service NHS Trust to enter into meaningful talks with Unite. The continuing refusal of the management to discuss patient safety - which led to the de-recognition of the union - has left our members with no option but to take further industrial action."
Yorkshire Ambulance workers are staging a fresh strike in a row over spending cuts. Members of Unite will walk out for 12 hours from midday with a further stoppage planned for June 22 if the dispute remains deadlocked.
The row centres on plans by Yorkshire Ambulance Service NHS Trust to make savings of £46 million over the next five years.
Unite, which has 500 members at the trust, said ambulance workloads were increasing by up to 6% every month.
Yorkshire ambulance workers have voted to hold a one day strike on Tuesday 2nd April. Members of the Unite union will work out because of a dispute over cost cutting measures which could see assistants with only six weeks training brought in to work with paramedics.
Union members also voted in favour of implementing a continuous overtime ban from 26th March.
Unite calls for the management to open constructive negotiations in the run-up to 2 April. This is a final window of opportunity for the trust to resolve this situation for the benefit of the Yorkshire public. The management has been trying to silence Unite after it raised legitimate concerns over patient safety that could flow from the shake-up of ambulance services in the next five years.
Now our members have voted for strike action on 2 April and for a continuous overtime ban from 26 March. It shows the depth of concern that our members feel about patient safety because of the £46 million of savings that managers want to implement. The hardline management has responded by derecognising Unite and twice rejecting our attempts to take this dispute to Acas and to discuss the implications of industrial action.”