The NHS's medical director in England, Sir Bruce Keogh, has warned junior doctors that their next strike will "irreparably damage" the public's trust in the profession.
Writing in the Observer, Sir Bruce said the decision to include emergency cover in the strike, went "against the grain" of the health service which promises to "do no harm".
Sir Bruce said that doctors were "the most trusted profession", and called this a gift.
The next industrial action by junior doctors is planned for 18 hours between 8am and 5pm on Tuesday April 26 and Wednesday April 27.
The British Medical Association (BMA) said junior doctors would be disappointed Sir Bruce was attacking frontline medics.
The BMA representative for junior doctors, Dr Johann Malawana, said none of his colleagues wanted to take the action but they had been "left with no choice" and called for the Government to resume negotiations.
He said: "Junior doctors would rather be in hospital, doing what they do, day in, day out: caring for patients.
"But they have already done everything else in their power to make their voices heard - protests, marches, petitions, emergency care only strikes. By continuing to ignore them, the Government has left them left with no choice."
Dr Malawana added that he regretted any disruption to patients and said that other doctors and staff would provide emergency care for those who need it.