Union chiefs have accused ambulance bosses of abusing a policy that allows them to cancel staff breaks.
Yorkshire Ambulance Service (YAS) declared a major incident last weekend due to the record volume of calls.
It received 4,082 calls of which 2,095 were categorised as immediately life-threatening.
YAS is reported to be rating itself as “critical”, just one short of the “potential service failure” ranking on a six-point scale measuring the pressures they face.
The surge of a third on normal levels on December 27 and 28 caused managers to invoke ‘MAJAX’ protocols, allowing them to force ambulance staff to work 10 or 12 hours without any rest and call in extra workers who were not scheduled to work.
Unison, the main trade union at YAS, has now claimed the move was not legitimate and said it will ballot for industrial action if it happens again.
New Year’s Eve and New Year’s Day is typically the busiest phase of the year for NHS urgent care.
A Unison spokesperson said: “The meal break policy states it can only be suspended due to a major incident.
“Staff feel the Trust is abusing them and their good will when they use the term ‘MAJAX’.
“The last true MAJAX, a single incident multiple casualty incident, YAS experienced was the Great Heck train disaster in February 2001.
“In both these cases staff were willing to go the extra mile without question, but some of those same staff who worked last weekend now feel that the trust are abusing them.”
The Great Heck rail disaster near Selby saw more than 80 people injured after a Land Rover swerved off the M62 on to the East Coast Main Line, causing a train to derail at 88mph.
Unison said it would “never agree” that ambulance staff should be forced to carry food on vehicles, take their breaks away from base station or have to eat at A&E departments.
The spokesperson added: “We are fully aware that demand has risen and the pressure this has caused but do not agree that working already exhausted members harder is the way forward.”
Ian Brandwood, Executive HR Director at Yorkshire Ambulance Service NHS Trust, refuted the claims that the Trust has misused the Major Incident protocol.
He said: “Over the last few weeks, as a result of unprecedented demand and more recently the adverse weather, the service has been under immense pressure and requests for help from those with potentially life-threatening illnesses or injuries has increased by almost 30%.
“When demand for our service exceeds the resources available to us we need to activate emergency procedures to allow us to continue to provide appropriate services to patients and one of those actions is to make changes to the delivery of staff breaks.
“Staff welfare is extremely important to us and, whilst this isn’t a decision which is taken lightly, it is necessary to maintain a safe level of service for our patients and every effort is made to ensure staff receive appropriate food and refreshments.
“During what is a very challenging time for all ambulance services, our focus is on reaching people with life-threatening illnesses and serious injuries as a priority and I would personally like to thank all of our staff for their support in ensuring life-saving help reaches those most in need. We continue to ask that members of the public use the service wisely and only call 999 in serious cases such as heart attack, breathing difficulties or stroke.”