Three council workers have lost their jobs for spending too long on the internet auction site eBay.
One was sacked and two resigned after managers at Neath Port Talbot Council found some staff were spending up to two hours a day on the website.
Union officials have blamed bosses for "putting temptation in their way" - by allowing access to the internet.
The council said it carried out an investigation after officials spent a "significant time" on the internet.
It said another two cases were being investigated while another member of staff had been given a warning.
Union officials said in all, over an 18 month period, up to six council staff had lost their jobs.
The council highlighted "an unacceptable level of usage of shopping, entertainment".
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 don't want them to use it in council time - at the end of the day they are employed to do a job of work not be shopping online."
The council, which employs 7,500 staff, had security software in place to prevent access to inappropriate websites such as porn sites but not eBay sites.
Andrew Woodman, regional organiser for Unison said they had asked for an urgent review.
"The council have gone completely over the top on this issue. The internet is part of our working lives, whether we like it or not."
Unison welfare officer Mark Fisher said people got "addicted" to certain websites.
"People get very involved in eBay, Sky Sports 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," he added.
The council has software to prevent staff accessing some sites
"We plan to push for the authority to make changes to its IT system, to help prevent workers landing themselves in hot water."
He called for internet access be limited to lunch break and that web access should be filtered at other times.
"We want them to take temptation out of people's hands," Mr Fisher said.
"These were decent well-paid jobs in admin earning between £20,000 and £25,000 a year.
"It is personally devastating to them to lose their jobs over this."
Employment solicitor Bethan Darwin, of Cardiff-based Darwin Gray Solicitors, said she regularly advised on excessive use of the internet which was a "constant problem for all employers".
She said some policies for companies also concerned the use of telephones for personal calls, mobile telephones and e-mail, and had become more commonplace in the last five years.
Ms Darwin said: "Technology is changing all the time, consequently workplace policies and procedures have to change alongside those developments."