Porn, gun and fetish sites blocked on council devices
Pornography, gun and fetish websites are among those Welsh council staff devices have been blocked from accessing.
Gambling, dating and subculture sites have also been blocked since January 2014, a Freedom of Information (FOI) request showed.
The public will "rightly question" such usage, the TaxPayers' Alliance said.
But the Welsh Local Government Association said only "a very small proportion" of workers breached rules.
Councils were asked to supply a list of sites staff had tried to access but were blocked from doing so while using work phones, computers, tablets and other devices since January 2014.
However, some councils said some of the sites disclosed may have been sponsored links, advertisements and pop-ups that staff had inadvertently tried to access.
Most of the data also did not show whether the sites were visited during working hours.
Information from Merthyr Tydfil council showed staff had been blocked from pornography sites and fetish websites.
In the past year, Pembrokeshire council workers were also blocked from accessing sites with sexual content.
During 2016, Newport council staff were stopped from visiting sites deemed inappropriate, including one featuring sex dolls.
Their devices were also blocked from a site "showcasing the world's largest collection of urinal photographs" and another on female bodybuilders.
A firearms market place site was also out of reach for Newport staff.
John O'Connell, chief executive of the TaxPayers' Alliance, said: "Taxpayers will rightly question why devices they are paying for are being used in such an improper fashion.
"Some employees will be working diligently and some will use the internet during their breaks but council bosses need to make sure that the equipment is being used in an appropriate way.
"As it stands it looks as if council staff are spending too much time surfing the web than getting on with the job they are paid for."
Numerous councils recorded staff devices being blocked from gambling, social media and shopping sites, such as Argos and Amazon.
News outlet websites, including those linked to the BBC, The Sun and the Daily Star, were also out of bounds for some.
Gwynedd, Cardiff, Rhondda Cynon Taff, Swansea and Vale of Glamorgan councils were either unable to supply the information or refused.
The Welsh Local Government Association said the internet was "for all organisations in the modern age" with social media being used by public bodies in a variety of ways.
A spokesman added: "However, local authorities have strict IT and internet usage policies for employees and particular types of sites are either flagged or blocked."
He said, while many local authorities allow personal use of the internet by staff outside working hours, it was their responsibility to ensure they used the internet "responsibly" and within relevant policies.
"There are often severe disciplinary implications should individuals be found to be in breach of such policies and councils therefore regularly monitor or block access to particular sites or types of site, as this data suggests," the spokesman said.
"Although the figures indicate a range of inappropriate sites that have been accessed by council employees in the past two years, they don't show how many individual employees have accessed such sites.
"Given the strict policies and processes that councils use, only a very small proportion of the over 140,000 local government workforce would have breached such policies and would have been disciplined as a result."