Rugby Australia has denounced homophobic comments made by Wallabies star Israel Folau warning 'sinners' are destined for hell.

Key points: Rugby Australia labelled the post "disrespectful" to members of the sporting community

Rugby Australia labelled the post "disrespectful" to members of the sporting community Israel Folau came under fire for similar comments made online last year

Israel Folau came under fire for similar comments made online last year At the time, he threatened to walk away from rugby if his beliefs were harming the game

Referring to an article about Tasmania's decision to legislate gender optional birth certificates, Folau took to Twitter on Wednesday afternoon to caution that "the devil has blindsided so many people in this world, REPENT and turn away from your evil ways".

Some two hours later, Folau — who last year garnered widespread criticism over similar comments — wrote on Instagram that "those that are living in Sin will end up in Hell unless you repent".

His comment accompanied an image, liked more than 8,000 times, that proclaimed hell awaits "drunks, homosexuals, adulterers, liars, fornicators, thieves, atheists and idolaters".

"Jesus Christ loves you and is giving you time to turn away from your sin and come to him," Folau wrote.

Rugby Australia said it was aware of the Instagram post and had engaged the Rugby Australia Integrity Unit to investigate.

"The content within the post is unacceptable," it said in a statement.

"It does not represent the values of the sport and is disrespectful to members of the Rugby community.

"The Rugby Australia Integrity Unit has been engaged on the matter."

'My faith is far more important to me than my career'

Folau, who spoke out against same-sex marriage after the Wallabies expressed support for the Yes campaign in 2017, previously said he was prepared to walk away from rugby if the situation became untenable due to his Christian beliefs.

Folau was heavily criticised for a post on Instagram last year in which he said God's plan for gay people was "HELL".

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He later said he had "no phobia towards anyone", but refused to back down on his beliefs, revealing he told ARU chief executive Raelene Castle he would quit rugby if his views were harming the game.

"This is not about money or bargaining power or contracts," he said at the time.

"It's about what I believe in and never compromising that, because my faith is far more important to me than my career and always will be."

The deeply religious player, who is a member of Assemblies of God church, was not formally sanctioned for his previous comments.

Rugby Australia will need to contend with a public figure's right to express personal views that many others consider offensive.