Patient care in England faces serious risks if the government pushes through planned hospital reforms, the British Medical Association (BMA) has warned.
The government wants all NHS hospital trusts to have achieved foundation trust status, which offers them greater independence, by 2014.
But the BMA has branded the timetable "foolish" and warned it will cause unavoidable and unacceptable risks.
Health Secretary Andrew Lansley insisted patient care will not suffer.
Dr Mark Porter, chairman of the BMA consultants' committee, said: "The push to foundation trust status for all is something that carries with it the unavoidable risk that the leadership of an NHS organisation will be focused on that above all.
"And that risk for patients I think goes too far."
In an interview for BBC Radio 4's File on 4, he added: "I feel really quite strongly that these artificial constraints imposed on the structure of NHS organisations are both wrong and detract from the primary mission which is the delivery of safe and effective health care to the local population."
Dr Porter's concerns have been echoed by Roy Lilley, a former NHS trust chairman, who called the coalition government policy "barmy" and "dangerous".
The foundation trust model was first introduced in England seven years ago. Scotland, Wales and Northern Ireland do not have the same system.
The aim was to give hospital managers, who were able to satisfy certain requirements, more financial autonomy and independence.
But a number of trusts which have already achieved foundation status are struggling with massive debts, management issues or failing patient care.
According to the health watchdog, the Care Quality Commission, of the 22 trusts where problems with care have been highlighted, 12 are foundation trusts.
And Monitor, the body in charge of assessing whether NHS trusts comply with the requirements of foundation trust status, said it had highlighted issues of concern with 17 trusts.
Health secretary Andrew Lansley hit back at the BMA, saying he did not believe patient care would suffer.
"Why is there a risk to patients? I simply do not accept that at all," he said.
Commenting on Care Quality Commission figures he added: "The Care Quality Commission is applying essential standards of quality and safety as part of their registration process and they apply exactly the same standards to NHS trusts as they do to foundation trusts.
"I believe in foundation status but I don't believe the purpose is as a badge of clinical quality.
"It's about them having freedoms, the corporate governance and financial strength to be able to improve their services in the longer term because of their financial and corporate strengths."
He has given NHS trust bosses until the end of next month to explain how they are going to achieve foundation status within the time scale.