Union leaders are to meet officials at the NHS Blood Service as part of their campaign against any moves to privatise the organisation.
A survey of 18,000 people published by Unite showed that three out of four opposed privatisation, including many who had previously donated blood.
The unions have criticised the government for failing to rule out privatising the service despite “massive” public opposition.
Unite national officer Jennie Bremner said: “Whether it is the frontline or the back office, privatisation of any part of the blood service contaminates the whole of the blood service.
“The people of this country are overwhelmingly opposed to privatisation. We expect the chief executive to give us a copper-bottomed guarantee that there will be no plans to allow private companies to profit from the blood service.
“It is totally wrong to allow private-sector companies to profit from men and women who freely donate their blood to help others. The message is clear - the people of this country say no to blood money.”
Unison has written to health minister Anne Milton calling for an urgent meeting to discuss the future of the blood service.
Unison’s assistant general secretary Karen Jennings said: “There are contradictory noises coming out of the government, but the message from the public is loud and clear - they don’t want the blood and organ donation service to be sold off.
“Donors give their blood in good faith. There’s no way a private company should be able to make money from this good will.
“Allowing private companies to take over stages of the donation process will break the smooth running of the service and have serious implications for blood safety.
“If the government isn’t planning to sell the service off, why are they inviting proposals from private companies? This government says it wants to be transparent but actions speak louder than words.”
A Department of Health spokesman said: “The review under way is exploring how further savings can be made and this includes continuing to outsource some activities. NHS Blood and Transplant will remain in the public sector - there are no plans to sell off any part of the Blood Service.
“We are not considering any functions that could risk destabilising the current national donor system. We have a wonderful system of altruistic donation of blood, tissues and organs in this country. We owe a huge debt of gratitude to all those who donate freely for the benefit of others.”