A fully-negotiated contract for junior doctors was "within reach", medics have said as they urged the Health Secretary to resume talks over the dispute.
In a letter to the Prime Minister, the Academy of Medical Royal Colleges' Trainee Doctors' Group said that an imposed contract posed a "significant risk to patient safety".
Royal colleges and unions have expressed dismay at Jeremy Hunt's decision, which came after weeks of deadlock between the British Medical Association (BMA), Government officials and NHS Employers.
"The Academy of Medical Royal Colleges' Trainee Doctors' Group (ATDG) condemns the Secretary of State for Health's decision to impose a new contract on junior doctors in the strongest possible terms and requests a return to negotiations with the BMA Junior Doctors' Committee immediately," the letter states.
The major sticking point has been over weekend pay and whether Saturdays should attract extra "unsocial" payments. Currently, 7pm to 7am Monday to Friday and the whole of Saturday and Sunday attract a premium rate of pay for junior doctors.
Under the new contract, 7am to 5pm on Saturdays will be regarded as a normal working day. Mr Hunt said the new contract will mean an increase in basic salary of 13.5% and that three quarters of doctors will see their take-home pay increase.
The letter states: "The determination to deliver immediate reform has meant that the final part of those negotiations concerning Saturday working have been curtailed prematurely.
"This is particularly distressing as we felt a fully negotiated settlement was within reach.
"The decision to unilaterally impose a contract in opposition to a significant proportion of the total medical workforce has further damaged the morale of an essential part of a profession that already feels undermined and under-valued.
"The stated aim in imposition is to restore certainty, but we caution that imposition has already generated further unrest amongst junior doctors and may precipitate an exodus of experienced staff from England to other jurisdictions within the UK and overseas."
The group also stressed that imposing contracts would mean that recruitment and retention of junior doctors would be much harder - especially in under-subscribed areas of practice including paediatrics, psychiatry, emergency and acute medicine and general practice.
The BMA has already staged two walkouts and further strikes and legal actions are possibilities, while some junior doctors may refuse to sign new contracts which are due to be implemented from August.
Commenting on the letter, Professor Derek Bell, president of the Royal College of Physicians of Edinburgh, said: "The ATDG have made it clear that they felt a fully negotiated settlement was attainable but imposing the contract is further undermining the morale of this hard working group of doctors and will be detrimental to the long term sustainability of the NHS in England.
"The junior contract alone cannot be seen as the solution to seven day working, which would require significant investment in staff and services across the sector.
"We hope that their legitimate concerns are acknowledged and addressed, otherwise any review of morale and working conditions will be meaningless."
The dispute has so far seen thousands of operations and appointments cancelled after junior doctors in England staged two strikes over the changes to their contract.
Commenting on the letter, a Department of Health spokeswoman said: "As Sir David Dalton set out in his letter last week, he saw no realistic prospect of a negotiated outcome.
"This is a fair, safe, reasonable contract - 90% agreed with the BMA.
"We have started the process to implement the contract, following calls from the NHS to end the uncertainty and agreement from NHS leaders that this is a fair and reasonable deal."