Michaela Banerji was fired in 2013 from the then Department of Immigration and Border Protection after it found she was behind an anonymous Twitter account critical of the agency.

Between 2006 and 2012, using the name "LaLegale", she posted 9000 tweets.

All but one were sent from outside the office and on her own mobile phone.

Following complaints by departmental staff, an investigation was launched into whether Banerji breached the public service code of conduct.

When she received her termination notice in September 2013 she suffered post-traumatic stress disorder and a month later lodged a workers' compensation claim.

The claim was refused on the basis that the sacking was "reasonable administrative action" - a decision which was affirmed by an internal review in 2014.

She then took it to the Administrative Appeals Tribunal, which found her termination was "not reasonable administrative action taken in a reasonable manner" and upheld her compensation claim.

As well, the tribunal found the public service's rules around the use of social media and making public comment "unacceptably trespassed on the implied freedom of political communication".

Compensation agency Comcare will take the case to the High Court on Wednesday, seeking a ruling that the tribunal erred in its interpretation of public service rules.

In its submission, it said anyone entering the public service must know the job "involves acceptance of certain restraints", an important aspect of is to "exercise caution when it comes to making criticisms of the government".

Having rules in place for public servants, who are meant to be apolitical, is not only consistent with Australia's form of government but "protects and enhances it".

Australian Associated Press