A Sydney telco employee has learned the hard way the perils of sharing too much information on Facebook after he was caught by his boss faking a sickie after a big night out.

In an email exchange doing the rounds of office blocks, Kyle Doyle was asked by his employer, AAPT, to provide a medical certificate verifying a day of sick leave in August.

Doyle, a call centre worker, protested, saying his contract stipulated he did not require a medical certificate for taking only one day off.