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.
Hunt added that there were plans in place to provide safe care, particular in maternity, A&E and crisis mental health services.
Hunt said: "We are proud of the NHS as one of our greatest institutions but we must turn that pride into actions and a seven-day service will help us turn the NHS into one of the highest quality healthcare systems in the world."
He added: "I wish to appeal directly to all junior doctors not to withdraw emergency cover, which creates particular risks for A&Es, maternity units and intensive care units."
He said he understood that some doctors may disagree with the Government over the new contract but said it offered doctors more premium pay than "police officers, fire fighters and nearly every other worker in the public and private sectors".
Hospitals across England are finalising plans for dealing with the first all-out strike by junior doctors in the history of the NHS. It will run from 8am to 5pm on Tuesday and Wednesday.
More than 125,000 appointments and operations have been cancelled and will need to be rearranged, according to figures from NHS England.
The BMA has defended the walkout, repeating its stance that it will call off the strike if Mr Hunt agrees to lift his threat to impose the contract.
Hunt has rejected this offer but wrote to the head of the BMA, Dr Mark Porter, over the weekend calling for an urgent meeting on Monday to discuss some parts of the deal.