Healthcare leaders have called on the British Medical Association (BMA) to call off the proposed series of five-day strikes by junior doctors later this month.
NHS Providers and the NHS Confederation, which represent NHS hospital, community, mental health and ambulance service trusts in England, said the planned action would lead to around 125,000 lost operations and over one million lost outpatient appointments.
Chris Hopson, chief executive of NHS Providers, said: "With barely any notice for trusts to prepare, this unprecedented level of strike action will cause major disruption and risk patient safety.
"NHS trust leaders agree with the Academy of Medical Royal Colleges that this action is disproportionate."
He added that less than 40% of junior doctors supported rejecting an agreement "strongly endorsed by their own representatives".
The medical regulator has urged junior doctors to seriously consider whether or not to take part in a new wave of strikes.
A five-day strike by junior doctors has been called in the ongoing dispute over contracts, but what does it mean for patients?