Labour will accuse the coalition Government of a "reckless gamble" with the NHS which the party claims will throw the service into chaos.
Shadow health secretary Andy Burnham will launch a national "defend our NHS" campaign, designed to highlight Labour's concern that the Government's plans spell "the end of the NHS as we have known it".
Health Secretary Andrew Lansley launched a reform White Paper earlier this month with promises to scrap unjustified targets, grant patients more choice, free hospitals from bureaucratic control and give GPs commissioning power, while phasing out strategic health authorities and primary care trusts.
But Mr Burnham was expected to say that the reorganisation is a £3 billion distraction at a time when the service should be focusing on its financial challenges.
Despite Government assurances that frontline health services will be protected, he claims that essential care is already being cut back while billions of pounds are spent on structural changes.
At a launch event attended by patients, healthcare workers and Labour members in Manchester, Mr Burnham will denounce the planned reforms as "unnecessary and dangerous".
In his prepared speech he will say: "It is an ideological experiment which threatens to unpick the very fabric of our precious NHS.
"It is a recipe for a postcode lottery writ large and signals the end of the NHS as we have known it. The chaos is starting now and I urge people to act now to defend our NHS.
"Right now, the NHS needs to focus solely on meeting the financial challenge. This unnecessary reorganisation will distract attention, reduce motivation and, scandalously, cost up to £3 billion - money that could have been spent on patient care."
Mr Burnham will cite reports of PCTs around the country being asked to shed 50% or more of staff before alternative structures are in place.