Three workers at Neath Port Talbot Council have lost their jobs because of excessive use of the internet while at work.
One employee was fired and two resigned after managers found that they were spending up to two hours a day on eBay.
Two other staff members are being investigated, and another has been given a warning about their online conduct. Seven staff managers have lost their jobs in the past 18 months.
Graham Jones, personnel chief at the council, said: "We have a policy of allowing employees to use the internet in their own time.
"But we clearly do not want them to use it in council time [as] they are employed to do a job of work and not to shop online."
Unison, which represents the workers, has accused the council of overreacting to the issue, and said that managers were partly to blame for allowing internet access to staff in the first place.
Mark Fisher, a welfare officer at Unison, acknowledged that people can get " addicted" to certain websites.
"People get very involved in eBay and their favourite soccer teams. It happens in many, many offices," he said.
"Obviously we cannot justify people spending a couple of hours of working time looking at these sites, but temptation was put in their way.
"We plan to push for Neath Port Talbot Council to make changes to its IT system to help prevent workers landing themselves in hot water."
The council did have software in place to allow for the blocking of violent or pornographic websites but not for mainstream sites.
"Most businesses allow some level of internet access during office hours, and this is crucial to many jobs," said Carole Theriault, senior security consultant at Sophos.
"But it is essential that employees are not allowed to run wild and spend as much time as they like on whatever happens to be their favourite site."
Theriault added that companies need to "nip the problem in the bud" before it can escalate into the kind of situation Neath Port Talbot council is experiencing.
"It is simple to block access to non-essential websites, and certainly a lot less embarrassing than having to sack or discipline staff," she said.
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