Government health reforms still pose an "unacceptably high risk to the NHS" and should be scrapped, according to the British Medical Association (BMA).
Chief among the BMA's fears is that foundation trusts will seek to generate far more income from private patients at the detriment of NHS services.
This would be made possible by the proposed removal of the cap on private income that foundation trusts are allowed to earn.
Howard Hughes, head of employee marketing at Simplyhealth, told COVER he also thought this could be the case.
Speaking about availability of choice to private patients, Hughes said: "There's always more choice than you might think.
"The NHS is there, which I think will get keener to provide private beds and other services."
Another of the BMA's main concerns is that the Secretary of State will not be ultimately responsible for running the NHS once the new proposals are enacted.
It noted the lack of satisfactory assurance that the Secretary of State will have ultimate responsibility for the provision of a comprehensive health service whilst also allowing other bodies, like the new NHS Board and clinical commissioning groups, day-to-day operational independence.
As part of its action against the Health and Social Care Bill, Dr Hamish Meldrum, council chairman at the BMA, has written to all MPs explaining the dangers that still exist within the legislation.
Although Dr Meldrum acknowledged government efforts to address some of the concerns expressed about the Bill, such as the listening exercise, but said this was not enough.
"We still believe the government's reform plans pose an unacceptably high risk to the NHS, threatening its ability to operate effectively and equitably, now and in the future," he wrote.
"This is why the BMA continues to call for the Bill to be withdrawn or, at the very least, to be subject to further, significant amendment."
"We believe there continues to be an inappropriate and misguided reliance on ‘market forces' to shape services."
Dr Meldrum continued by calling the new proposals short sighted and overly complex.
"Insufficient thought has been applied to the unintended knock on effects and long term consequences of proposals in the Bill, including for medical education and training, public health and the patient-doctor relationship," he wrote.
"There is now excessive complexity and bureaucracy associated with changes made to the Bill to counter the lack of proper checks and balances in the original proposals.
"Furthermore, much detail is still lacking, being left to subsequent regulations and guidance," he added.
The body has also called for a day of action on 5 September before the Bill passes through two stages in the House of Commons and then on to the House of Lords.
It has asked the general public and health workers to bombard MPs with emails and use twitter and Facebook to voice concerns about the Bill.
