Employers should allow their workers to befriend, chat and "poke" each other through online networking sites while at work, Britain's largest labor federation said Thursday.

While accepting that employers were within their rights to block employees from using sites such as Facebook and MySpace, the Trades Union Congress, or TUC, said a ban "may be something of an overreaction."

"Sensible employers, realizing that their staff spend much of their waking hours in work and lead busy lives, should be trusted to spend a few minutes of their lunchbreak 'poking' their friends or making plans for outside work," the TUC said in guidance published on its Web site.

Online social networking sites — where users sign up, make friends and post photos — have grown rapidly in Britain. Facebook Inc. recorded more than 7 million unique British visitors in July, according to online measurement company comScore Inc. MySpace.com Inc. and Bebo Inc. had more than 10 million visitors each. In all, the top three social networking sites drew as many visitors as Google Inc., according to comScore.

The sites can be a headache for employers and educators — especially when users affiliated with a school or company post inflammatory, indiscreet or just plain embarrassing content. Organizations as diverse as the Ministry of Defense and Oxford University have issued guidance on using the sites within the past month.

The TUC said bosses needed to give their employees guidance on what was and was not acceptable online, rather than imposing a ban. It warned that, in the absence of any workplace rules, British Facebook users were "3.5 million accidents waiting to happen."

"It's unreasonable for employers to try to stop their staff from having a life outside work, just because they can't get their heads around the technology," TUC General Secretary Brendan Barber said in a statement. "Better to invest a little time in working out sensible conduct guidelines, so that there don't need to be any nasty surprises for staff or employers."'

The TUC also warned employers against searching through the Web profiles of job applicants, saying doing so could end up being discriminatory.

The TUC, an umbrella organization for Britain's trade unions, says it represents more than 6.5 million workers.

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