The hearing process will involve a panel of three - a representative of RA, a representative of the players' union RUPA and an independent person approved by both organisations, who would be the chair.
The religiously-motivated Folau posted: "Warning".
"At its core, this is an issue of the responsibilities an employee owes to their employer and the commitments they make to their employer to abide by their employer's policies and procedures and adhere to their employer's values", Castle said.
It is not the first time the star player has had a run in with authorities over his social media use.
Rugby Australia bungled its contract negotiations with Israel Folau by failing to insert social media restraints, according to a Sydney media report.
"As a code we have made it clear to Israel formally and repeatedly that any social media posts or commentary that is in any way disrespectful to people due to their sexuality will result in disciplinary action".
Folau, who signed a new four-year contract back in February, was given 48 hours to accept the sanction or have the matter referred to a Code of Conduct hearing.
The fundamentalist Christian posted similar comments a year ago but escaped sanction and signed a new deal with RA through 2022 in February.
"Why's everyone so anxious about what Israel Folau said, " Hopoate wrote.
Folau has won 73 caps and was expected to play at this year's World Cup in Japan.
Folau says hell awaits drunks, homosexuals, fornicators and others.
Now a pundit on Fox Sports, Drew Mitchell has all but called his former Australia and NSW Waratahs colleague a hypocrite, posting on Twitter Folau's comments from a year ago saying he would walk away from the game if Rugby Australia found his position untenable.
Widely considered one of the game's best players, Folau is Super Rugby's all-time leading try scorer. Hell awaits you. Repent! "Jesus Christ loves you and is giving you time to turn away from your sin and come to him", the player wrote on Instagram on April 10, along with a series of biblical scriptures.
The same day, he linked on Twitter a story about Tasmania allowing those ages 16 and over to change their birth certificates or to remove gender from the certificates altogether.