The Finance Department's John Sheridan told a gathering of public servants in Canberra that rules for the behaviour of federal public servants were clear and reasonable, and departments were entitled to act when they were broken.

Mr Sheridan said public servants on Twitter and Facebook were no different to other workers using a noticeboard to disparage their employers.

"If you spend time bagging your organisation online or offline, you should not think that your employment is going to continue unconditionally," he told the audience.

"You shouldn't be surprised by the consequences."

"If you post defamatory material on a pinboard in the office, this behaviour should be treated in the same way as posting that material online."

His comments followed news that the sacking of Immigration Department official Michaela Banerji appeared all but certain, over harshly critical comments she made on Twitter against her employer, albeit anonymously.

The Federal Court refused on Monday to grant a stay of dismissal to Ms Banerji, who was in the audience to hear Mr Sheridan's comments.

Another bureaucrat, the Foreign Affairs Department's Darryl Morris, also looks certain to be sacked over the activities of a Facebook group of which he is allegedly a member.

Mr Sheridan told the forum, hosted by the Institute of Public Administration Australia's ACT division, that public servants were bound to remain impartial in political matters.

"The public service centres upon principles of impartiality, so that we can provide services to whatever side of politics holds government at a given point," he said.

Fairfax Media revealed on Tuesday that the Immigration Department's combative spokesman, Sandi Logan, himself a target of Ms Banerji's tweets, has had his online voice silenced by the new Abbott government.