NHS England is set to hand over its patient data and share of a £480m contract to US company Palantir in a plan to create a new database.
This marks the biggest IT contract the NHS has ever awarded.
Palantir is a spy technology firm that works with intelligence and military agencies in the UK and US, including the CIA.
UNISON is working alongside the campaigning organisation Foxglove to help challenge this. An emergency petition to health secretary Victoria Atkins has been set up, which UNISON members are invited to sign and share.
The petition calls on Ms Atkins to cancel the contract and design an NHS data platform that keeps the NHS public, respects patient choice and protects privacy.
UNISON policy officer Guy Collis said: “NHS data is far too important to be sold off in this way and patients are rightly concerned. It’s not too late for a rethink.”