A leading union today launched legal action against the Government over its health White Paper, claiming ministers failed to consult over its plans to "fundamentally change" the way the NHS is run.
Unison said it wanted to challenge Health Secretary Andrew Lansley over his "refusal" to consult with the public on proposals in the White Paper, which was published last month.
The union said the plans would bring about the most fundamental changes to the way the NHS operated since it was created.
Unison said that the day after the White Paper was published, NHS chief executive Sir David Nicholson wrote to all NHS chief executives instructing them to start implementing the proposals "immediately", which the union maintained was unlawful.
Officials argued that no steps should have been taken to implement the changes until the public had been given the opportunity to comment on them.
Karen Jennings, Unison's head of health, said: "I find it incredible that the NHS chief executive would say he believes there is no legal duty on the secretary of state to consult on the merits of the proposals in the White Paper.
"The White Paper contains sweeping changes to the NHS and how it should be run. The NHS constitution enshrines the principle that the public, staff and unions have an absolute right to be consulted, and that means not only on how the proposals are to be implemented, but also whether they should go ahead in the first place.
"The Department for Health's refusal to recognise this clear and important legal duty leaves us no option but to issue legal proceedings as a matter of urgency."
Unison claimed the White Paper opened the door to privatisation of the health service, warning it would plunge the NHS into "chaos".
Ms Jennings said: "Far from liberating the NHS, these proposals will tie it up in knots for years to come - they are a recipe for more privatisation and less stability.
"NHS staff will feel badly let down by plans to undermine national pay bargaining. In a race to do this, the Government wants employers to lead negotiations on new contracts resulting in a two-tier workforce within Trusts and anomalies across the NHS."
Unison criticised plans to cut back on bureaucracy and do away with Primary Care Trusts and Strategic Health Authorities while allowing the "proliferation" of GP consortia and giving billions of pounds to "untried, untested and probably private sector-led" organisations.
Shadow health secretary Andy Burnham backed Unison, saying: "There is no democratic mandate for the break-up of the NHS. I don't believe there are many, if any, of the seven million people who voted Lib Dem who support the Government's plans. As the Coalition Agreement explicitly ruled out a top-down NHS reorganisation, these dangerous plans represent one of the biggest and quickest U-turns in political history.
"The gains in the NHS have been hard won and cannot be thrown away by this high-handed and arrogant Government. Patients tell us they do not want a return to a postcode lottery and longer waits but that is precisely what these plans will lead to.
"GPs are unprepared for it, NHS staff don't want it and patients never asked for it. With a price tag in the billions and reports of frontline cuts growing, the public must have a say in whether they want this reorganisation, given that the two coalition parties did not tell them about it at the election.
"It is scandalous that the Government is preparing to spend up to £3 billion on this reorganisation at a time when the NHS needs stability, and when every single available penny should be directed towards maintaining standards of patient care."
A Department of Health spokesman said: "The White Paper sets out a clear strategy and sustainable structure for the long-term future of the NHS. It gives NHS staff and the patients they serve a clear sense of direction and purpose. The Government is engaging fully with the public, healthcare professionals, local authorities and unions on how its proposals will be implemented.
"The Government has already launched public consultations on specific elements of the White Paper, and further documents will be published this year. NHS chief executive David Nicholson has written to encourage the NHS to begin locally led consultations and take first steps on the implementation of the White Paper, without pre-empting the wider consultation. Many reforms are also subject to Parliamentary approval as part of the Health Bill.
"Through the proposed changes, healthcare professionals and patients will have more power to shape, lead and deliver local healthcare services, away from the control of central Government."