Almost 400 public health experts have given the government's NHS reforms a damning review.
They believe the Health and Social Care Bill "will do irreparable harm to the NHS, to individual patients and to society as a whole" and accused it of encouraging commercialisation of the service.
As a result, they called on the House of Lords to stop the Bill's progress.
A letter published in the Daily Telegraph also reiterated that the reforms do not have support from medical practitioners and their representative bodies, despite claims by Prime Minister David Cameron otherwise.
However, the PM tried to claim the letter supported the reforms, telling the BBC: "When you look at the letter itself, it actually praises the part of the Bill that's about public health.
"Because we're saying public health - smoking cessation, diet, dealing with things like diabetes - these are incredibly important and they welcome that part of the Bill."
He did acknowledge that there are doctors in the health service who did not like the proposals.
Signed by nearly 400 public health doctors and specialists, the letter voiced their concerns about the current proposals.
"The Bill will do irreparable harm to the NHS, to individual patients and to society as a whole," they wrote.
"It ushers in a degree of marketisation and commercialisation that will fragment patient care; aggravate risks to individual patient safety; erode medical ethics and trust within the health system; widen health inequalities; waste much money on attempts to regulate and manage competition; and undermine the ability of the health system to respond effectively to communicable disease outbreaks and other public health emergencies.
"While we welcome the emphasis placed on establishing a closer working relationship between public health and local government, the proposed reforms will disrupt, fragment and weaken the country's public health capabilities.
"The Government claims that the reforms have the backing of the health professions. They do not. Neither do they have the public's support.
It concluded by saying: "The Health and Social Care Bill will erode the NHS's ethical and cooperative foundations and will not deliver efficiency, quality, fairness or choice. We ask the House of Lords to reject passage of the Health and Social Care Bill."
A Department of Health spokesman responded: "Our plans to modernise the NHS will give patients more choice, root out waste and give trusted NHS staff more power to improve care.
"A group of the country's top doctors and NHS experts have already analysed the Health Bill and we have accepted all their recommendations to improve it. Many GPs and other doctors have also already spoken out in support."