The Department of Health has rejected claims that it plans to privatise areas of the NHS blood service.
The DH is leading a review into the “commercial effectiveness” of NHS Blood and Transplant but said there were no proposals to privatise the blood service.
A spokesman said: “During the review we will be considering the experience and skills that exist in the private sector to identify opportunities for making NHSBT more commercially effective.
“Part of this will involve talking to private providers about what NHSBT could do differently to realise efficiencies without impacting the safe supply of blood and blood products to the NHS. It is not a procurement or tendering exercise.
“We are not considering any functions that could risk destabilising the current national donor system, particularly the interface with donors.
“Any options that are identified will be considered very carefully before a final decision is made by ministers.”
A petition against any such plans has been signed by more than 25,000 members of the public in less than a week.
Unite said its campaign had struck a chord with the public, adding that people were right to be concerned about the prospect of private providers running parts of the service, including transportation and storage of blood supplies.
Assistant general secretary Jennie Bremner said: “Yesterday alone 7,000 people signed the petition and we expect the numbers of people joining our campaign to grow. Men and women, young and old alike are really angry about the government’s plans.
“Donors help save the lives of hundreds of thousands of people every year including cancer patients, accident victims and women giving birth who develop complications.
“Anyone who can see the clear moral contradiction in giving blood freely to help others for it then to be used for profit by the private sector should get behind Unite’s campaign to urge David Cameron to stop the blood money.
“The message is getting louder by the hour as more people join the campaign - our blood is not for sale.”