Some attendants have already received warning letters for grumbling about duty rosters, passengers, their bosses and colleagues, according to the Straits Times newspaper, quoting news agency AFP.

On one Facebook account, a woman calling herself an SIA flight attendant said she was "going to be upset" if she was called up for "lousy" flights to Sydney, Melbourne and Hong Kong on Airbus A380 super-jumbos.

"No fair... roster no good again... no fair," said another account.

"So many flights.. So little Off Days.. I’m going crazy..." a third Facebook user remarked.

An SIA Spokeswoman is quoted as saying: "Our staff may of course have a blog or Facebook and Twitter account like any other member of the public.

"But our policy is clear that they must not comment on work matters about business or customers, so as to protect proprietary information as well as the privacy of other staff and our customers."

A posting on the SIA staff union website stated that "recently, there have been a few cases of crew being penalized for their postings on Facebook about company-related matters such as their rosters".

"Please refrain from such postings on your Facebook wall or any public forums or blog, as you do not know who is really lurking out there and who are really your friends," it added.