A group of 40 charities says the government's plans for health changes in England must be revised to give a voice to the most vulnerable patients.
They say the current proposals fail to ensure that patients will be properly consulted in the planning of services.
The charities have issued a statement setting out six "much-needed" changes.
The coalition government says there will be substantive changes, and describes feedback from organisations such as these as "invaluable".
This statement has a long and impressive list of signatories, including the Alzheimer's Society, the Patient's Association and the National Autistic Society.
The charities set out a series of demands designed to ensure that the public, patients and carers have a say - especially those least able to speak up for themselves.
"Seeking out views"
That means requiring GP consortia - which will handle most of the NHS budget - to be proactive in seeking out their views.
They also call for changes to improve the links between health and social care, a stronger system of patient advocacy, and better access to specialised services for people with complex needs.
The statement says the uncertainty surrounding the NHS does not help anyone, but it welcomes the government's listening exercise.
"The Department of Health needs to use this time to substantially improve the Health and Social Care Bill," it says.
Patient Association chief executive Katherine Murphy said the organisation was constantly hearing on its helpline from people who were worried about the changes.
"Patients are worried about GP commissioning - will GPs deviate from the clinical to the commercial? Will they be referred on to the best services or those that are going to make their GP more money? Will the changes mean shorter appointment times with GPs as they have to focus on balancing the books?"
Mencap's chief executive, Mark Goldring, said it was vital to ensure that the health system worked for the most vulnerable patients.
"It is essential that the government keeps patients at the heart of NHS reforms and ensure that the most vulnerable in our society, such as those with a learning disability, have access to the good quality healthcare they need."
National Autistic Society chief executive Mark Lever called for greater clarity.
"We need a clearer indication from the Department of Health about exactly what the future will look like for NHS services", he said.
The charities' intervention comes just a day after Deputy Prime Minister Nick Clegg said that the right kind of reform came "from the patients' point of view".
In a statement a Department of Health spokesperson said: "We agree that patients need to be at the heart of modernising the NHS - this has always been the central aim of our plans. But we recognise that there have been some concerns, and feedback from organisations such as these is invaluable to make sure we get this right.
"The health secretary has been clear that there will be substantive changes to the bill if they deliver improvements for patients. We await the recommendations from the NHS Future Forum, expected next month."