No more slating your employer online - firms and employment tribunals are finally getting to grips with social networking

Thinking of badmouthing your employer or work colleagues on a social networking site? After the case of the Apple employee, whose dismissal for doing just that was this week upheld by an employment tribunal, you'd be well advised to think again.

On the face of it, social networking outlets such as Facebook and Twitter might appear to offer people an arena for venting their spleen on any issues, including gripes and grievances about work.

But although they may well be your own private views, such forums are often viewable by anyone, and you may face repercussions from your employer if you choose to write about work issues, regardless of whether it's from your desk, home or mobile phone.

Many companies now have a social media/blogging policy as part of their contractual terms with employees, providing clear limitations about the permissible contents of a blog. This may also limit use of your work PC to access social media websites (or other sites) during work hours.

Such policies put employers in a much stronger position when they want to take action against employees writing things they don't approve of. In serious cases, giving vent to your feelings about work could amount to gross misconduct and, therefore, instant dismissal.

Employment tribunals are starting to get to grips with the use of social media sites, and have recently upheld a number of dismissals against employees for gross misconduct relating to blogging about work.

In the case of the Apple worker, his colleague (also a Facebook "friend") told his boss about the offending posts. Apple has a very clear social medial policy prohibiting employees from making critical comments about its brand on social media sites, which undoubtedly helped the company win the tribunal.

In another recent case, a Metropolitan police officer was sacked for posting "deeply offensive messages" about a colleague on Facebook. You would expect to be disciplined if you acted in this way face to face, so why not in the cyber world?

Some would argue that the ability of an employer to reach out even to private blogs smacks of Big Brother. However, there is an implied term of "trust and confidence" incorporated into every contract of employment, together with a further obligation not to bring your employer into disrepute. Such implied terms override the "where, when and how" such comments are made.

It is not just careless comments on social media sites that can land you in trouble. There have been numerous instances of employees facing disciplinary action for criticising bosses or work colleagues verbally or otherwise.

There is a big difference between harmless banter and comments that go to the heart of the employment relationship and thereby undermine that all-important "trust and confidence" term in your contract. It will be a matter of fact and degree in every case and some will be easier to determine than others.

Relevant factors would include whether the employer was identifiable, the impact on the employer's image, the nature of the comments posted, and who was privy to them (if customers or clients, this would surely work against the employee).

In this harsh financial climate, there are bound to be a tetchy relationships at work, but there is a fine line between what is acceptable and what is not. If you cross the line and unreasonably badmouth your employer or work colleagues, you could find yourself out of a job.

Philip Landau · guardian.co.uk