Attorney-General Christian Porter launched a defence of a government decision to sack an Immigration Department worker for anonymous tweets about Australia's asylum seeker policy, and sought to justify the burden it imposed on free expression.

In a case that could weaken or entrench the bureaucracy's limits on political commentary from public servants, lawyers for the Attorney-General told the court on Wednesday the restrictions protected and enhanced responsible and representative government.

The freedom of speech implied in Australia's constitution accommodated the need for an apolitical public service and rules enshrining the importance of the bureaucracy, Solicitor-General Stephen Donaghue, arguing for the government, said.

These combined to suggest that "burdens on political communication by public servants may be more readily justified than similar burdens on other groups," he said.

"The imposition of such burdens on public servants promotes the functioning of the system of government for which the constitution provides."

Public servants work under rules requiring them to uphold the bureaucracy's integrity, impartiality and good reputation, and governments have limited their free political expression in Australia since before federation.

An appeals tribunal decision in April threw into question the federal public service's ability to enforce limits to free speech, finding the Immigration Department's 2013 dismissal of former bureaucrat Michaela Banerji was unlawful because it intruded on her right to free political expression.

Mr Donaghue denied the Australian Public Service prohibited its staff from holding or expressing opinions, but said rules designed to promote a professional bureaucracy, willing to serve governments of different political views, put justified limits on their free speech. 

Public servants had to work in a detached manner, unaffected by their political beliefs, but they could still hold views. The limits to their expression extended as far as required by a code designed to keep their workplaces impartial and professional.

"The burden upon political communication arising from the code is not correctly identified as a prohibition on APS members expressing political opinions. The code is more nuanced," Mr Donaghue said.

He also rejected an Administrative Appeals Tribunal finding that guidelines stopping public servants from publicly criticising the government should not be applied to anonymous comments.

"While a communication that is critical of the APS may have more weight if known to have been made by a member of the APS, such statements may damage the 'good reputation' of the APS even if it is not known who made the relevant communications," he said.

Exempting anonymous comments from rules limiting bureaucrats' free political speech would raise problems for the government by creating an "area of immunity" for misconduct.

Mr Porter intervened in the case after Ms Banerji won an appeal against the federal workplace insurer's refusal to compensate her for the psychological condition that developed after she was sacked over tweets from a pseudonymous Twitter account with the handle @LaLegale.

He removed the government's Federal Court appeal against the finding and sent it to the High Court, flagging the case's potential to undermine the government's policy stopping public servants from expressing their political views on social media.

Ms Banerji was working in the Immigration Department when co-workers learnt she was behind tweets railing against the government's treatment of asylum seekers.

She lost a high-profile attempt to stop her dismissal in the Federal Circuit Court in 2013, a decision seen as likely to curtail other bureaucrats' use of social media when judge Warwick Neville found Australians had no "unfettered implied right (or freedom) of political expression".

Her tweets did not disclose confidential departmental information, but an internal Immigration Department investigation in 2012 found she had breached the code of conduct for government employees.

Lawyers for Ms Banerji are expected to respond to the Attorney-General's arguments in early December.