Nirmal Singh took action for unfair dismissal after his employment was terminated in October last year by Aerocare Flight Support, a national aviation services company contracted by Virgin Australia.

Aerocare had concerns a Facebook post by Mr Singh saying "We all support ISIS" could result in "panic, furore and concern about public safety" and damage the reputation of Aerocare and Virgin, the Fair Work Commission heard.

Mr Singh had made the comment above a Facebook post he shared from religious extremist group Hizb ut-Tahrir, which has known sympathies with ISIS, about a demonstration in Lakemba.

But he claimed the post, made under the pseudonym Sherri Solace Singh, was "sarcastic" and "no one in Australia supports ISIS beliefs or its activities".

Aerocare alerted the Australian Federal Police to the October 4 post and an investigation was carried out by the Joint Counter Terrorism Unit, which attended the company's offices at Perth Airport. It terminated Mr Singh's employment on October 8.

Greg Shelley, Aerocare's general manager for employee relations, gave evidence the AFP were "regularly patrolling the airports and we have had a number of instances where people have allegedly made jokes that have been banned by the airline from flying".

"With respect, we can't accept, 'I was just joking', after the event as an explanation," Mr Shelley said.

"It's not treated that way with passengers, it's not treated that way with baggage. If somebody was to write, even jokingly, on an aircraft that there was a bomb on board or something like that the terminal would be evacuated in accordance with the procedures."

But in a decision on Tuesday, Fair Work Commissioner Jennifer Hunt said Mr Singh's dismissal was "harsh, unjust and unreasonable" although it was an "incredibly stupid" comment that breached the company's social media policy.

While the post did "not even have the look of sarcasm" and was not "witty" or "funny", Commissioner Hunt found "a more thorough investigation ...[of Mr Singh's Facebook page] would have satisfied Aerocare that Mr Singh did not support ISIS".

"A reasonable conclusion would be then that the ISIS post was an incredibly stupid post to have been made," she said.

Commissioner Hunt added her finding "should not suggest that it is acceptable for employees in the relevant airport environment to post what appears to be support for a terrorist organisation and explain it away as sarcasm, comedy or satire".

She said Aerocare had also sought to rely on posts that did not breach its social media policy to bolster its decision to sack Mr Singh. This was not "a valid reason for dismissal", she said.

There was no evidence Aerocare had considered any other sanction apart from sacking Mr Singh.

If it had carried out a more thorough investigation of the post, it would have been appropriate to meet with Mr Singh, reiterate the company's social media policy and warn him that any subsequent breach of the policy would result in the termination of his employment, Commissioner Hunt said.

Commissioner Hunt found Mr Singh's casual employment was unlikely to continue for an extended period of time. She awarded Mr Singh $4,800 less tax in compensation, an amount equal to eight weeks' pay less 40 per cent for misconduct.