Jeremy Hunt has appealed to junior doctors not to withdraw emergency cover during their strike but said "no trade union" has the right to veto a Government manifesto commitment.
In a clear sign that he will not back down just hours before an all-out strike by medics across England, the Health Secretary said changes were needed to create safer services at weekends.
Referring to the British Medical Association (BMA), he said "no trade union has the right to veto" a manifesto commitment made by the Government to improve weekend services.
In a statement to MPs, he said the disruption over the next two days was "unprecedented" but the NHS has made "exhaustive efforts" to ensure patient safety.
Mr Hunt added that there were plans in place to provide safe care, particular in maternity, A&E and crisis mental health services.