The doors could shut on 13 libraries as council chiefs look to tackle a major funding gap over the next three years.
The library services faces a £847,000 funding shortfall
Dorset County Council has revealed it is looking at "radical" plans to close the rural libraries to save money.
It is trying to tackle a £20m budget shortfall by 2009. The library service itself has an £847,000 gap in funding.
Union bosses said they were "disappointed" closures were being planned and said talks were being held to avoid compulsory redundancies.
Alan Martin, regional officer for Unison, said: "This affects up to 60 staff.
The possible closures
"Unison has a proud tradition of campaigning for decent public services. We will want to campaign alongside Dorset communities in their battle to safeguard their libraries and other essential services.
"The closure of these 13 libraries is set to save the council up to £850,000 over the next three years but at what cost to the rural communities and those that run the libraries?"
Alan Havelock, the council's cabinet member for libraries, said the council could not "sustain the current library network in the medium to long term".
He added: "The view is that a major change to our service now, giving the potential for reinvestment, would be much better than gradual reductions to the service over a number of years, which would not give any chance to reinvest at all.
"Painful though some of the changes will be in the short-term, we believe that a realistic, if radical, approach now would be less disruptive to the services, customers and staff in the long run."
If the closures are given the go ahead by the council's cabinet on 12 July, the existing mobile library service will be extended.