The issue of social networking in the context of employment has reared its ugly head once again, this time in relation to English football's biggest club, Manchester United. The club recently issued a statement on its website advising fans that none of the Manchester United players "own" any social networking sites, despite the fact that at least three first-team players – including Ryan Giggs, Darren Fletcher and Wayne Rooney – were believed to run personal Twitter sites. The club has stated that it warns players not to engage in social networking, although whether it specifically instructed the players to close their sites is unclear.

The statement follows a number of high-profile disputes arising from the use of Twitter by other Premiership footballers. In July last year, Darren Bent almost scuppered his transfer from Tottenham Hotspur to Sunderland after criticising the Tottenham chairman Daniel Levy on Twitter during the negotiation stages. Earlier in January, Liverpool's Dutch striker Ryan Babel complained on Twitter about being dropped without explanation from the squad, which prompted an angry response from his manager Rafael Benitez.

The risks involved in using such sites are obviously not limited to sports stars and other celebrities with their public image in mind. Across the world, the number of cases involving employers who have disciplined staff for allegedly misusing sites such as Twitter and Facebook, either within or outwith working hours, continues to increase. A throwaway comment about your manager's short fuse, a bigoted remark about a colleague, an unflattering photo from the office Christmas party posted on your page, or a rant about the job you are working on at the moment to an online "friend" could easily result in an employer taking disciplinary action.

One of the most significant employment issues arising from the widespread proliferation of social networking sites is that the vast majority of companies' employment contracts and additional policies covering the acceptable use of electronic media do not adequately cover social networking. For example, many policies cover the use of email and internet facilities within the workplace, but do not provide for "out of hours" activities or the use of social networks.

At the other end of the scale, it is quite possible that a tribunal or court could find a policy unenforceable on the basis of it being too restrictive on employee activities, particularly where a policy covers the use of blogs or other networking sites outside of working hours and in respect of non-work blogging. Employers should therefore strive to find a balance between protecting their own interests (upholding the company's reputation, preventing confidential information being publicised, and maintaining good relations in the workplace) and allowing for the freedom of expression. It is vitally important that employers review their disciplinary and acceptable use policies to ensure they reflect changes in online behaviour, to minimise the risk to business.

But it's not all about red cards or red flags, despite the inherent risks involved in allowing employees to use social networking sites in their free time, social networking can be a useful way of promoting your company and should not necessarily be viewed in a negative light.