More than 300 people have signed a petition protesting Croydon Council's decision to hire a private company to run the borough's libraries.
The council last month confirmed 13 public libraries would be outsourced to John Laing Intergrated Services (JLIS) after a protracted tendering process.
JLIS, which has been awarded an eight-year contract, will take the reins from October this year.
But campaigners have launched a last-ditch bid to stop the move.
A petition, launched by Save Croydon Libraries, has been signed by 341 people so far.
Elizabeth Ash, who started the petition, said: "This is our last chance to save Croydon's libraries.
The public have never been consulted on the outsourcing of our library service, which is due to go through imminently.
Serious concerns have been raised about the tendering process and the company which is due to run the libraries. Repeated requests for information have been refused.
We have to let Croydon Council know that they cannot and must not ignore the wishes of the residents that they serve."
The council claims the libraries contract will save it money in the long term.
You can sign the petition here.