Staff at libraries across Bromley have gone on strike in a row over pay.
The action by more than 30 workers is affecting 14 venues in the borough.
Talks aimed at ending the dispute broke down on Monday with union members describing the pay offer as "insulting".
In reponse Greenwich Leisure Limited which operates the libraries for the council said:
“It is most regrettable that after keeping dialogue with Unite open to the 11th hour, the union is continuing with plans for strike action.
“Unite represents under a quarter of library staff in Bromley and our priority is to maintain a ‘business as usual’ service – all Bromley libraries are open today.
“GLL is a worker-owned charitable social enterprise which puts the community and our staff at the heart of our public services. We have committed to pay London Living Wage in Bromley.
“The union demands are not sustainable.”