A public servant sacked for tweeting criticisms of the federal government raised suspicions among colleagues who noticed her desktop image resembled her Twitter profile picture, federal government lawyers say.
Solicitor-General Stephen Donaghue told the High Court former Immigration Department worker Michaela Banerji was not protected by her anonymity when she posted politically-charged comments online.
At a hearing for the case testing public servants' free speech on Wednesday, Mr Donaghue defended the limits on political expression that brought on her 2013 dismissal, saying they protected the bureaucracy's impartial role.
He denied rules restricting public servants from making political comments aimed to rid them of opinions or targeted their free speech.
Lawyers for Ms Banerji, who argue the restrictions don't apply to anonymous comments, say the Immigration Department risked its own reputation by outing her as the source of the tweets railing against government policies.
Ron Merkel, representing Ms Banerji, said rules requiring public servants to uphold the bureaucracy's apolitical, impartial character did not apply to anonymous comments.
"Anonymity is essential to whether or not there was a breach," he said.
Mr Donaghue told judges Ms Banerji made little effort to conceal her identity within the department itself and colleagues became suspicious when they saw her computer desktop at work.
"The notion of anonymity is one that has a little more complexity than it might seem entirely in the abstract," he said.
Restrictions on political communication may be more readily justified when applied to public servants than to other groups, Mr Donaghue said.
The limits these put on free speech protected democracy by keeping the public service apolitical and letting it advise the government and implement policy effectively. Freedom of speech implied in Australia's constitution accommodated the need for an apolitical public service.
Mr Donaghue said the restrictions were not a blanket prohibition on political communication from bureaucrats but only applied to the extent the rules upheld the bureaucracy's impartial role.
"They do so in a particular way to promote a particular character of the public service," he said.
Ms Banerji's lawyers wrongly argued that anonymity at the time of writing exempted her from the restrictions and stopped her comments from damaging the government, Mr Donaghue told the judges.
Her lawyer's arguments would mean a public servant criticising ministers would be immune from sanction provided they were anonymous at that time, even if they were later identified, he said.
Public servants could use anonymity because they knew their comment was damaging to the government, Mr Donaghue said.
The damage might be compounded by the fact governments could not sanction public servants or address their behaviour.
"Once the identity of the person is known, the damage by the behaviour of the person is manifest, and it may at that point be necessary to take a decision under the code to alleviate the harm."
Mr Donaghue said arguments that anonymous comments were protected also failed to explain situations when the public servant's identity might be known by some people, despite the use of a pseudonym.
Restrictions on free speech for public servants gave a wide scope for decision makers to account for individual situations in deciding any penalties, he said.
High Court judges are hearing the case after the Administrative Appeals Tribunal last year found Ms Banerji's dismissal unacceptably trespassed on her freedom of speech. Attorney-General Christian Porter sent the case to the High Court in a move showing its potential to weaken limits to political commentary among bureaucrats.
The matter continues on Thursday, when Ms Banerji's lawyers are expected to present their case.