Ambulance staff are due to go on strike again this afternoon.
Members of the Unite Union, who work for the Yorkshire Ambulance Service, will walk out between 3pm and 8pm.
It claims its members will go 10 hours without a meal break and be forced to work 12-hour shifts by changes to working patterns introduced last month.
People are being urged to use the emergency service wisely and only dial 999 in an emergency.
David Whiting, chief executive for the Yorkshire Ambulance Service NHS Trust, said: “Our plans to maintain high standards of patient care and minimise any impact from previous episodes of strike action have been effective and we have taken steps to ensure our service remains just as resilient this time.
“We would like to reassure members of the public that our contingency plans continue to focus on providing a safe, responsive and high-quality emergency service which remains the Trust’s top priority.
Mr Whiting said 999 should only be used for ambulances when someone has a life-threatening or serious illness or injury. Anyone requiring advice or treatment for a non-emergency situation or minor ailment should consider things like self-care, a visit to a local pharmacist, contacting the NHS 111 urgent care service or going to their GP, a walk-in centre or minor injuries unit.”
To find your nearest non-emergency service, visit http://www.nhs.uk/service-search or call 111.