In a statement, Rugby Australia described content within the post as “unacceptable” and said its integrity unit was looking into Folau’s conduct.
The Wallabies star was warned last year, but avoided any disciplinary action, for making homophobic comments on his social media channels.
A message published on his Instagram account on Wednesday read that “hell awaits” for “drunks, homosexuals, adulterers, liars, fornicators, thieves, atheists, idolators.”
Folau said on Instagram: “Those that are living in Sin will end up in Hell unless you repent. Jesus Christ loves you and is giving you time to turn away from your sin and come to him.”
Rugby Australia responded in a statement, which read: “Rugby Australia is aware of a post made by Israel Folau on his Instagram account this afternoon.
“The content within the post is unacceptable. 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 tonight.”
Folau, 30, was reminded of his social media obligations by RA chief executive Raelene Castle last year.
There were also threats from sponsors of the Australian national team that they would withdraw support following his social media posts.
Kirsty Clarke, director of sport at Stonewall, also condemned Folau’s actions.
“Tackling offensive language is a crucial part of helping LGBT people feel welcome in sport,” she said. “Folau’s comments are just one example of how much work is still left to do to combat discrimination and the use of hateful language against lesbian, gay, bi and trans people.
“It’s important that Rugby Australia have stepped up to challenge Folau’s abusive comments.”