David Cameron is facing pressure to allow healthcare professionals to take part in tomorrow's summit on NHS reforms.
Labour leader Ed Miliband accused the Prime Minister of failing to listen to the experts as it emerged major bodies critical of the proposals have not been invited to the Downing Street meeting.
Mr Cameron called the summit to discuss the implementation of the Health and Social Care Bill, which faces intense opposition and has yet to reach the statute book.
But some organisations most critical of the bill, such as the British Medical Association (BMA) and the Royal College of General Practitioners, appear not to have been invited.
Downing Street would not disclose who had been invited to attend the meeting, saying only that it was a "range of national healthcare organisations and clinical commissioning groups".
A spokeswoman said it was being held "to discuss implementation of the health reforms with representatives from a range of national healthcare organisations and clinical commissioning groups.
"This forms part of the Government's ongoing dialogue with health practitioners about the implementation of these reforms."
The BMA said it would be "odd" if bodies representing health professionals were not invited to the summit.
"The BMA does not appear to have been invited to an NHS summit at Downing Street," a spokesman said.
"If there is such an event, it would seem odd if the major bodies representing health professionals were not included."
The Chartered Society of Physiotherapy (CSP), another opponent of the bill, said it had not been invited to tomorrow's summit.
Chief executive Phil Gray said: "It is extremely concerning that many of the key professional bodies and healthcare organisations, which will be expected to work with the changes that the bill will bring, have been excluded from what is clearly a crucial meeting.
"If new legislation is to succeed it is vital that those raising concerns are listened to and it is disappointing to see that so many organisations are being shut out of the process."
In his criticism of the Prime Minister, Mr Miliband told the Welsh Labour conference: "You don't get progress on the NHS by shutting the door of Downing Street on doctors, nurses and patients' groups.
"It's not the actions of a Prime Minister to exclude from an NHS meeting the people who are the experts on the health service.
"The Prime Minister should listen to these experts and drop the bill."
Wales' First Minister Carwyn Jones told the conference in Cardiff that Mr Cameron should find the "humility" to admit his party's proposals to reform England's NHS were wrong.
Members of the Royal College of Paediatrics and Child Health have joined several Royal Medical Colleges, including the Royal College of GPs and the Royal College of Radiologists, in calling for the bill to be scrapped.
Unions, including the BMA, the Royal College of Nursing (RCN) and the Royal College of Midwives (RCM) are among those also calling for the bill to be withdrawn.
Mr Cameron reaffirmed his support for the bill last weekend after reports that three Tory Cabinet ministers were against it and influential website Conservative Home urged him to drop it.
He insisted he was "at one" with his beleaguered Health Secretary Andrew Lansley.
Critics say the proposed reforms are effectively privatisation of the health service by the back door - and prompted more than 142,000 people, including footballer Rio Ferdinand and TV star and author Stephen Fry, to sign a petition calling for the bill to be scrapped.