A campaign group backed by the late Professor Stephen Hawking will begin its High Court challenge against Jeremy Hunt over plans to allow private companies to play a greater role in the NHS.
The JR4NHS group was founded by three doctors and a university professor, and supported by the renowned physicist until his death in March.
Prof Hawking had warned that introducing commercial companies to run parts of the health and social services would amount to an "attack on the fundamental principles of the NHS".
A judicial review by the four remaining claimants against the introduction of accountable care organisations (ACOs) is due to begin in London on Wednesday.
The campaigners say ACOs will "Americanise" the NHS and set the boundary of what care is free and what has to be paid for - and that they will be paid more if they save money.
Mr Hunt's Department of Health and Social Care has rejected claims about ACOs as "irresponsible scaremongering".
NHS England is due to hold a national 12-week consultation on the contracting agreements for the ACOs, which supporters say will help to better co-ordinate care and improve patient services.
However, when announcing his support for the legal action in December, Prof Hawking said the NHS "must be protected from those who want to privatise it".
He said in a statement at the time: "I am concerned that accountable care organisations are an attack on the fundamental principles of the NHS.
"They have not been established by statute, and they appear to be being used for reducing public expenditure, for cutting services and for allowing private companies to receive and benefit from significant sums of public money for organising and providing services."
JR4NHS was founded by former consultant eye surgeon Dr Colin Hutchinson, public health professor and doctor Professor Allyson Pollock, Dr Graham Winyard CBE, a former medical director of NHS England, and public management professor Sue Richards.
The four said in a statement they "continue to be inspired" by the way Prof Hawking continued to fight for the NHS right up to the end of his life.
In a statement in January following the grant of permission for the judicial review, a Department of Health and Social Care spokeswoman said: "We strongly resist the misleading claims in this action; it is irresponsible scaremongering to suggest that ACOs are being used to support privatisation and harm the fundamental principles of the NHS.
"The NHS will remain a taxpayer-funded system free at the point of use; ACOs are simply about making care more joined-up between different health and care organisations.
"Our consultation on changes to support ACOs is entirely appropriate and lawful.
"We believe it is right that local NHS leaders and clinicians have the autonomy to decide the best solutions to improve care for the patients they know best - and any significant local changes are always subject to public consultation and due legal process."
The hearing, before Mr Justice Green, is expected to last for two days.