NHS patients' watchdogs facing the axe have said they have been "overwhelmed" by public support for their work.
The Board of Community Health Councils (CHCs) in Wales claimed a national council set to replace them would have no remit to listen to people or the power to hold anyone to account.
The Welsh Government said such a body would have "the necessary functions and powers to carry out that role".
It also denied Conservative claims that the consultation had been "cosmetic".
Under the proposals, a single body could replace the existing seven CHCs, which carry out spot checks on hospitals and represent patient interests.
The Board of CHCs accused ministers of releasing its plans "quietly" as the assembly broke up for the summer.
Its chairwoman Mutale Merrill said despite this, the board sought public views over the summer and found support for "a stronger people's voice" which was independent, could hear directly from people, and "has the teeth to challenge care providers when they find that improvement is needed".
She said: "We've been overwhelmed by the number of people who took the time to talk to us about the proposals and how they wanted to be represented in future."
The board said the CHCs agreed a new body was needed with a remit over health and social care.
But it said they had "serious concerns" the Welsh Government's plans would deliver "a people's voice body with no remit to listen to people and no power to represent their interests or hold organisations to account on the service they deliver".
Meanwhile there has been criticism about the extent to which the public has been included in the debate about the proposals.
A three-month consultation was launched at the end of June, and a series of eight "informal focus groups" are being held until 29 September.
But a Facebook post, found by the Welsh Conservatives, suggested one of the organisers of the events was still looking for venues and participants on 2 September, just under a month before the consultation ends.
Rhion Jones, director of the Consultation Institute - a body which advises authorities on how to engage the public - welcomed the focus groups but said the decision to hold them was "belated".
"So far, there has not been sufficient debate," he said.
"Abolishing a major part of the NHS structure in Wales is of such importance, and the proposals for a replacement body so unclear - some would say 'vague' - that it has cried out for transparent public sessions at which ministers and/or officials could explain precisely what they have in mind."
The think tank said the Welsh Government declined an invitation to a paid-for event it held in Cardiff in September, on the grounds that it could affect the integrity of the consultation.
Conservative AM Mark Isherwood claimed the consultation had amounted to "little more than a cosmetic exercise".
"The lack of urgency Welsh Government has accorded to organising these vital engagement events - not to mention the lack of opportunity for stakeholders on all sides of the debate to properly express their views in publicly accessible events - completely undermines the legitimacy of this process," he said.
"I cannot discount the possibility of pursuing judicial review in the event that a deadline extension is not granted."
A Welsh Government spokesman said: "It is important to recognise that proposals in the White Paper are not only about CHCs, but should be viewed together as a package of potential measures designed to not only strengthen the voices of people who use health and social care services, but also to improve the quality and governance of those services in Wales.
"We are pleased the CHC Board acknowledges the need for a new body but clearly we want the consultation responses to inform the detail around any new arrangements and to hear from a wide cross-section of stakeholders on all the proposals.
"Whilst the proposals relating to public voice in the White Paper are quite high level, it goes without saying that we would of course want to ensure that any body set up to represent citizens in health and social care has the necessary functions and powers to carry out that role.
"This is something we will be developing, in conjunction with stakeholders, once the consultation has closed."
The Welsh Government also said it it was "not true to say there has been a failure to properly engage and at no point have CHCs asked for any extra time".
"The consultation, which has had 250 responses so far, has been underway since 28 June and we have offered to meet key stakeholders including the CHC board," a spokesman said.
He pointed to an earlier consultation over the 2015 Green Paper Our Health, Our Health Service.