Israel Folau launched legal proceedings against Rugby Australia over the termination of his contract on Thursday, casting the action as the pursuit of his "right to religious freedom".

Folau, a fundamentalist Christian, was sacked by Rugby Australia and his Super Rugby club New South Wales Waratahs last month for a post on social media that said hell awaited "drunks, homosexuals, adulterers" and other groups.

The 30-year-old former Wallabies fullback said he would seek a declaration from Australia's Fair Work Commission, an industrial relations tribunal, that his employment was terminated because of his religion.

"No Australian of any faith should be fired for practising their religion," he said in a statement that confirmed his case had been lodged.

"Ours is an amazing country built on important principles, including freedom of religion.

"A nation made up of so many different faiths and cultural backgrounds will never be truly rich unless this freedom applies to all of us."

Rugby Australia and New South Wales Rugby later released a joint statement defending their decision.

"It is important to make clear that (we) did not choose to be in a position where (we) are forced to divert significant resources to defend the ongoing legal action taken by Israel, but his action leaves the game with no choice," it read.

"This is an issue of an employee and his obligations to his employers within the contract that he signed.

"He was bound by a Code of Conduct for all professional players in Australia that spells out clear guidelines and obligations regarding player behaviour, including respectful use of social media."

Folau confirmed this week that he had engaged commercial law firm Macpherson Kelley and a prominent industrial relations barrister to act for him in his dispute.

He was found guilty of a "high level" breach of Rugby Australia's code of conduct by a three-member tribunal after a prolonged hearing last month.

His four-year contract, worth up to A$5m (€3.10m) according to local media reports, was torn up but he waived his right to an appeal, saying he had "no confidence" in Rugby Australia's judicial process.

His statement on Thursday said his termination had prevented him from playing at the "peak of his career" and on the cusp of a Rugby World Cup, which could have generated greater exposure and opportunities.

"Accordingly, Mr Folau is seeking substantial remedies from his former employers should they be found to have breached the Fair Work Act in terminating his employment," it said.

A dual code international, Folau switched to rugby union in 2013 and scored 37 tries in 73 tests, while claiming the John Eales medal as the country's best player a record three times.

Local media have reported that he is seeking a return to the 13-man code in Australia's National Rugby League but the sport's boss Peter Beattie said he would not sanction his return.