The wellness caput said "voluntary arrangements" for exigency screen during caller ambulance strikes could not "ensure diligent and nationalist safety".
In a missive to the GMB, Steve Barclay acknowledged unions that walked retired had agreed to reply the astir superior class 1 999 calls.
But helium said the deficiency of screen for class 2 calls, including strokes, successful immoderate areas enactment lives astatine risk.
The GMB has accused the authorities of "demonising" its striking workers.
The national represents much than 10,000 ambulance workers who went connected onslaught connected Wednesday crossed 9 ambulance services successful England and Wales.
On Saturday, successful an unfastened letter to Prime Minister Rishi Sunak, the GMB said his authorities had "singled retired ambulance workers arsenic portion of a crude effort to region our close to strike".
It added: "You are making america and our ambulance colleagues consciousness demonised."
In response, Mr Barclay wrote connected Sunday that helium recognised the close to onslaught and accepted "that a definite magnitude of disruption is inherent to immoderate strike".
He said helium "greatly" valued the "vital enactment ambulance workers do" but criticised the "volatile" assurances fixed to him astir screen by commercialized unions during December's concern action.
The authorities would acceptable minimum work levels for fire, ambulance and obstruction services during concern enactment and could permission unions astatine hazard of ineligible enactment if they neglect to comply.
In his letter, seen by the BBC, the wellness curate acceptable retired wherefore nationalist minimum work levels should beryllium acceptable successful instrumentality during "blue light" strikes, which helium said had the imaginable to "put lives astatine contiguous risk".
"During caller enactment I person not been reassured that the existent strategy of voluntary arrangements tin beryllium relied upon to guarantee diligent and nationalist safety," Mr Barclay wrote.
He said the arguable Strikes Bill would supply the nationalist with "much needed assurance that a definite level of urgent and time-critical attraction volition ever proceed passim onslaught action".
Mr Barclay denied it deprive workers of the close to strike, but alternatively would "reflect that immoderate individuals volition not beryllium capable to onslaught astatine definite times truthful that a minimum work level tin beryllium maintained".
Under the caller legislation, employers would beryllium required to contented enactment notices 7 days earlier onslaught enactment and lone aft consulting with commercialized unions.
The GMB said its ambulance committee planned to sermon the wellness secretary's missive astatine its gathering connected Monday and would see its response.
Ambulance unit are scheduled to locomotion retired again connected 23 January.