Opponents, who branded the move an "abdication" of Shropshire Council's responsibility, today said they had taken legal advice.
Twelve libraries could close in the near future unless community groups come forward to take over their running. Another six large face a review of their management with a view to offloading them.
The proposals were passed by the council's cabinet at Shirehall.
Council cabinet member Councillor Steve Charmley insisted the idea behind the plan was to keep libraries open, adding: "The last thing we want to do as a council is to be closing libraries."
Under the plans, libraries at Albrighton, Bayston Hill, Broseley, Cleobury Mortimer, Church Stretton, Ellesmere, Gobowen, Much Wenlock, Pontesbury, Shawbury, Shifnal, and Wem, will close unless community groups come forward. The management of Bridgnorth, Ludlow, Market Drayton, Oswestry, Shrewsbury, and Whitchurch libraries will be reviewed.
Shropshire Libraries Yes campaigner, Michael Green, warned councillors at the meeting that the decision could now face a legal challenge and called for talks.
He said: "We are not prepared to stand by while our library service is disassembled. We have taken advice from a leading public administration lawyer. There is a high likelihood of our being granted a judicial review under legal aid."
George Candler, the council's director of commissioning, said the policy was in line with the aim of moving towards a commissioning approach – where it pays other groups or companies to provide services.
But Labour councillor Alan Mosley said the proposals were an "abdication" of responsibility, adding: "This is not a long term plan, this is a patch up, you are abdicating responsibility for what is a hallowed and valued service for the community."
End of story unclear for countys libraries
Shropshire's libraries face an uncertain future as community groups must now consider taking them on.
The proposal will also see a review of the management of six large libraries, including the historic building in Shrewsbury as well as Bridgnorth, Ludlow, Market Drayton, Oswestry and Whitchurch.
Looking for new management and delivery for the larger principal market town libraries and customer service points: Bridgnorth, Ludlow, Market Drayton, Oswestry, Shrewsbury, Whitchurch.
Libraries that Shropshire Council wants community organisations to run, with some council funding: Albrighton, Bayston Hill, Broseley, Cleobury Mortimer, Church Stretton, Ellesmere, Gobowen, Much Wenlock, Pontesbury, Shawbury, Shifnal, Wem.
Smaller libraries already under alternative management: Craven Arms, Bishops Castle, Highley libraries.
Libraries where Shropshire Council is looking for community groups to take over management of customer service points, with some council finding: Albrighton, Bishops Castle, Broseley, Church Stretton, Ellesmere, Shifnal, Wem.
Customer service point under new management: Craven Arms.
Mobile library service: Review of current service in 2016. There are currently four mobile libraries covering 350 communities on a fortnightly basis.[/breakout]
There were mixed views on the proposals expressed at the cabinet meeting. Kevin Richards, a representative of Shawbury, warned that with no-one prepared to take over the village's library it is set for closure.
However, a representative of Cleobury Mortimer, said that they had looked more favourably at the proposals as they would allow the community to retain a library.
The Friends of Ellesmere Library are considering whether they can take control of their library. But the group's chairman, John Shone, told councillors he did not believe enough consultation had been carried out on the strategy of asking community groups to take responsibility for libraries. He questioned why the council had not considered a trust taking over all the libraries.
However, George Candler, the council's director of commissioning, said that the approach had been set out in a consultation on commissioning services 18 months ago.
More than 40 people have attended a consultation into Ellesmere Library's future and Steve Charmley, the council's cabinet member responsible for libraries, said they were open to any proposals put to them to keep libraries open.
Mr Candler added: "We have a level of interest in alternative suggestions and even though there is an end date on the Ellesmere consultation if alternative ideas come up we will want to investigate those before we come to a conclusion."
Shifnal Town Council has also been speaking to residents over plans to take control of a number of town features, including the library. The town council held a consultation meeting yesterday at the library to discuss residents' thoughts on the proposals, which could see the council moving from its rented premises to the library.
Councillor John Murray, mayor of Wem, has rejected the idea that the council should take over more Shropshire Council services.
He said: "We have done enough volunteering in Wem. We have volunteered to run the town hall and swimming pool.
"It should be Shropshire Council's responsibility to keep the library going."
A public meeting organised by the Albrighton and District and Civic Society to discuss possible ways of saving the village library was attended by 70 people on Monday. One of the options to see it continue is for the parish council to move into the building, saving costs.