UNION officials have pledged to fight the loss of more than 250 North-East jobs.
The public sector union Unison said staff at the Durham branch of the Prescription Pricing Authority (PPA) had been left "stunned and uncertain of their future".
It follows Tuesday's announcement of job losses by the PPA.
Only last month, the NHS announced it would be creating more than 800 jobs in Newcastle by merging up to four of its operations, including the PPA, to form a new Business Services Authority.
However, when that announcement was made it was not made clear that this would also involve the closure of the PPA processing centre, in Durham City.
On Tuesday, PPA staff were told that job losses were inevitable because of technological improvements which could see a national reduction of the workforce by two-thirds and the number of sites reduced from eight to three.
Workers have been told that the jobs will begin to go from October next year until March 2007.
Peter Chapman, Unison regional officer, said: "The scale of these redundancies and the timescale have come as a great shock.
"A lot of Unison members have worked at the PPA for a considerable length of time and could well have difficulty finding alternative employment."
Liz Twist, Unison regional head of health, said: "We will be campaigning at all levels to oppose the plans."
Nick Scholte, chief executive of the PPA, said: "Every penny the PPA saves is another penny for patient care in the NHS."
He said it was "inevitable" that jobs would go, adding that the authority would aim to minimise the impact.
A spokesman said a number of options would be considered including the possibility of redeployment.
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