Workers using internet blogs and podcasts to talk about their employers increasingly face the sack, legal experts have warned.

According to Littler Mendelson, the largest employment law firm in the US, the risk of bloggers being fired is rising rapidly as companies clamp down on leaks of commercially confidential information.

The legal firm warned that few companies have written policies which include references to employees' blogs and podcasts, but said that this does not prevent employees from being axed for telling the internet world what is on their minds or divulging company data.

Littler Mendelson cited recent firings at Google and Delta Airlines in the US which have cast the spotlight on these "thorny legal issues".

"Employees can have a false sense of security when it comes to postings," said Christopher Cobey, senior counsel in Littler Mendelson's Silicon Valley office.

"They mistakenly believe that if they shroud the blog or podcast with anonymity, they are immune from the consequences.

"However, in most states employment is 'at-will', meaning that employers can fire an employee without cause. Learning that an employee is disloyal to the company may be all an employer requires to exercise its option to terminate the person's employment."

Cobey suggested that companies incorporate blogging and podcasting policies into existing guidelines on confidential information, trade secrets and use of company electronic resources.

The legal expert also warned blog authors that using company time or computers to update their sites may be in violation of company policy. And blogging at home about one's employer, even on personal time, can in some circumstances result in being sacked.

If an employer is discontented with an employee's blog, the employee's removal of the inappropriate content or the entire site may not even be enough to remedy the harm.

As soon as the information is made public by internet posting, the content can be copied and posted to other sites without the original writer's knowledge or permission. "Once the cat is out of the bag, it's hard to unring the bell," Cobey added.