Ambulance chiefs have admitted that many 999 calls in Yorkshire are re-assessed.
But they insisted that all decisions made by the Yorkshire Ambulance Service are to help patient care.
The confirmation comes after concerned paramedics voiced fears over 999 calls being downgraded in order to meet targets.
They have called on independent inspectors from the Care Quality Commission to look at the system, which they claim is putting people at risk.
The YAS issued a full statement today on the issue and insisted there are already regular checks in place.
But the health union Unison said figures in a Freedom of Information request to the Yorkshire service revealed that almost 11,0000 calls were re-classified last year, about 30 a day. Some got a faster response but others were downgraded.
But a Unite spokesman said it still saw the Yorkshire service miss the target of getting 75% of ambulances to “Red” emergencies in 11 out of 12 months between October 2013 and last October.
Unite general secretary, Len McCluskey said: “What Unite has uncovered is absolutely alarming. There needs to be a thorough investigation into allegations that the service could be gambling with people’s lives. Senior management at the Yorkshire Ambulance Services have a record of systemic failure, incompetence and are mired in allegations of cover-ups”.
A YAS spokesman said: “The Trust’s main priority is to provide a high-quality ambulance service in Yorkshire and the Humber and we work very hard to ensure that we provide an appropriate and timely response to all of our patients.
“In some life-threatening emergencies it may be beneficial to patients to receive further in-depth clinical assessment. Highly-skilled clinicians based in the Emergency Operations Centre provide further assessment, advice and support using nationally-validated support tools.
“This clinically-led process may identify that the patient’s condition is more or less serious than the initial assessment. This results in those with a serious condition receiving support from a clinician until an ambulance clinician arrives on scene and those whose condition is not immediately life-threatening receiving the most appropriate care for their need where alternative pathways of care are available.
“In addition, less urgent calls are assessed by clinicians to ensure that they receive the most appropriate response for their needs.
“Processes in the Emergency Operations Centre have been independently audited on a number of occasions including a Care Quality Commission review in 2013 as part of its routine inspection regime when it was fully satisfied with the processes in place, a Peer Review by the Association of Ambulance Chief Executives (AACE) in 2014 and an NHS West Yorkshire Audit Consortium review on behalf of the Trust’s commissioners in 2014”.