Hundreds of NHS workers are set to protest against plans to close blood centres across England.
Opponents fear patients will be put at risk
Demonstrations are planned outside many centres including those in Leeds, Birmingham, Sheffield and Southampton.
Unions are campaigning to halt plans to centralise work in three centres in London, Bristol and Manchester.
The union Amicus has voted to take industrial action but the National Blood Service denies patients will be put at risk by the changes.
Amicus official Owen Granfield said: "If we only have three sites in the UK, it would be impossible to maintain the right levels of blood stock and patients may go short of blood products and services."
Bill Campbell, national officer of Unison, said it was wrong to make cuts in a "life-saving service".
"Closing centres will mean precious blood supplies will have to be transported from one end of the country to the next.
"This is not only riskier, but will undermine the service's ability to cope with emergencies such as the London bombings, putting people's lives in further danger.
"The National Blood Service should look again at these proposals and make their decisions on what will help to save the most lives, not what will save the most money."
The National Blood Service dismissed claims that the reorganisation would potentially put patients at risk.
It said it planned to maintain a network of local blood banks, so patients would continue to get the blood and blood components they need when they need them.
Peter Garwood, managing director, said: "We have had a good look at the service we are providing to the NHS, and our plans are designed to ensure an efficient supply of safe blood for patients in the future.
"Whilst we are planning to consolidate processing and testing into three centres, all services that need to remain close to patients will do so.
"We will also make the blood collection service much more convenient for donors, to fit in with their lives."