A Norwich MP claims 20 people died after ambulances arrived late during a 12-day period of intense pressure on the emergency service.
Clive Lewis, who represents Norwich South for Labour, told the House of Commons a whistleblower had contacted him to raise concerns.
He said the constituent told him how senior operational managers had wanted to move East of England Ambulance Service to its highest state of alert - REAP 4 - on December 19.
The Resource Escalation Action Plan is designed to maintain an effective and safe operational and clinical response for patients - and could have involved calling in help from the armed forces.
But a final decision was not made until December 31 - and even when it had moved to REAP 4, the trust did not seek aid.
In response, the East of England Ambulance Service admitted "some people experienced a delay in their care over the festive period" because of "significant pressure".
Mr Lewis raised the matter in the Commons as a point of order - addressing it as a question to Speaker John Bercow about how to get a response from the Health Secretary.
Mr Bercow suggested Mr Lewis should table questions to the Health Secretary and consult colleagues on the Labour frontbench.
"He's aired his concern and it will have been heard on the Treasury bench," he added.
Earlier this month, ITV News Anglia revealed how a pensioner had been found dead in her house after waiting more than three hours for an ambulance to arrive.
The 81-year-old woman called 999 at the beginning of January - not during the time period mentioned by Mr Lewis - complaining of chest pains.