The council has followed a number of organisations to ban Facebook
A council is to ban Facebook on its computers after it was revealed staff spent on average 400 hours on the site every month.
Portsmouth City Council said it had decided to change its policy and block access to the social networking site.
It added the figures equated to each of its 4,500 staff, who have access to computers, spending between five and six minutes a month on the site.
The Taxpayers' Alliance said the move would stop the "waste of public cash".
Mark Wallace, from the group, added: "It is sad that it has reached a point where councils need to ban staff from Facebook.
"But people are employed to work hard for the taxpayer and this is clearly a waste of public money."
The council stressed it was unable to determine whether staff had been accessing Facebook in break times or before or after work, which had been allowed.
The ban will come into force in the next few weeks and will also see the Bebo, Twitter and eBay sites blocked - YouTube had already been banned.
David Williams, chief executive of Portsmouth City Council, said: "We regularly revise our position on this as the internet environment is constantly changing.
"We revised the policy in July to facilitate work life balance and allow things like internet banking in staff's own time but we intend to restrict internet access to social networking sites more than at present for non-business use.
"Any member of staff may, under this revised policy, make a business case to have these sites unblocked if they need to use them for council business."
Other organisations have also brought in a Facebook ban.
But in March, Hampshire County Council only issued a threat to block the site after it found 46 employees were regularly spending more than an hour on the site each day.