Israel Folau's sacking by Rugby Australia (RA) has set the scene for a potential court battle that will test religious expression and freedom of speech in Australian sport.

Key points: Israel Folau is yet to decide if he will sue Rugby Australia for breach of contract and religious discrimination

Israel Folau is yet to decide if he will sue Rugby Australia for breach of contract and religious discrimination Athletes seem unclear what they are permitted to say regarding their religious beliefs

Athletes seem unclear what they are permitted to say regarding their religious beliefs Australia's peak body for sports unions has called for clarity over an athlete's rights over freedom of religious expression

Folau's social media post warning homosexuals (among others) of the hell that awaits them has cost him his four-year contract worth millions of dollars.

More than that, it has caught sport off guard over freedom of religious expression and is forcing all Australian sports to examine the clarity and validity of their own codes of conduct.

Folau is still deciding whether to sue RA for breach of contract and religious discrimination.

The Rugby Union Players Association (RUPA) pointed out to RA that players still do not know what they can and cannot say regarding their religious beliefs.

Israel Folau has refused to take down the controversial Instagram post that led to his sacking. ( Supplied: @izzyfolau )

"[RA] has not yet provided any clear or specific parameters to the professional playing group specifying how it expects individual professional players to express their faith and beliefs in manner acceptable to [RA]," RUPA said in a statement.

The association is now taking it upon itself to try to get some clarity by setting up its own review.

When Queensland Reds captain Samu Kerevi posted on social media: "Thank You Jesus for dying on the cross for me", it set off a firestorm that saw the Australian rugby union international initially apologise for the post, then clarify that he did not need to apologise.

It pointed to the state of confusion among the players.

AFL player and devout Christian, Gary Ablett, has previously expressed his religious beliefs on social media. ( AAP: Dave Hunt )

Not just a rugby problem

Clarity is needed not just for rugby union players, but for all religious sportspeople who have publicly expressed their faith.

They include Folau's wife and New Zealand netball international Maria Folau, AFL player Gary Ablett, Parramatta NRL captain Tim Mannah and rugby union's Sonny Bill Williams.

Sydney University professor in law Ron McCallum said the termination of Folau's contract for what he calls "hate speech" is a "warning to players in other codes".

Most sports have codes of conduct and social media policies. Most are also expressed generally: players can't bring the code into disrepute, they must use social media responsibly and not discriminate or vilify.

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Professor McCallum said the codes needed to be more specific and social media policies should be included in contracts.

"They should say things like players are free to express their views on religion, but they are not free to discriminate, insult or hurt other people," he said.

The Folau case has thrown up the question of where the boundary lies between discrimination and religious freedom.

It is a matter that could very well be tested under Australia's Fair Work Act if Folau takes his case to the Federal Court, citing religious discrimination.

"The live legal question is how far can an employer go in curbing an employee's activities outside working hours or [in their] personal lives and how do you draw that distinction in the first place," Sydney University senior lecturer in employment law Giuseppe Carabetta said.

"Rugby Australia have been very careful in stating that their reason for terminating is because in their view he breached the code of conduct.

"As a general proposition, making the code clearer would help in this respect."

Which is why Australia's other sporting codes are watching developments very closely.

Rugby league in particular, like rugby union, has a high proportion of strongly religious players from the Pacific community.

"When it comes to providing players with clarity regarding what is appropriate to share on social media and how this can be delivered, we are of the view that there is always more work that can be done," a Rugby League Players Association spokesman said.

But the chairman of the Australian Rugby League Commission, Peter Beattie, thinks the situation is crystal clear.

"I don't think there are any players who play rugby league [who] would be under any doubt about our inclusiveness and what our rules are," Beattie said.

Other sports are on notice

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It is not just league and union watching closely.

The general secretary of the peak body for the country's sports unions, the Australian Athletes Alliance, Jacob Holmes, said all sports and players needed clarity so players knew their "rights and responsibilities are fair, reasonable and comprehendible".

The ABC also contacted the AFL, Cricket Australia, Netball Australia and Football Federation Australia, as well as various players' associations.

The majority of the associations said they were aware of the Folau case, but expressed their confidence in their respective codes of conduct and their education processes.

But if the Folau saga has taught us anything, it is that the murky intersection of social media, contracts, freedom of religion and freedom of expression is anything but black and white.

Vaguely worded codes of conduct may not be enough. In the future the rules will need to be written in stone.

Professor McCallum said the sports want certainty.

"They want your property," he said.

"They're buying you body and soul."