According to the Racial Discrimination Act, it is illegal to behave offensively toward a person because of race, colour, national or ethnic origin.
The definition doesn't apply to religion - and that's a problem according to the Grand Mufti of Australia, Ibrahim Abu Mohammed.
Dr Mohammed made a submission to the parliamentary freedom of speech inquiry, saying that unless the clause was expanded to include religion, members of faiths like Islam would be subjected to hate speech and vilification.
"This will create a disharmonious environment for minority groups in Australia and have a negative impact on multiculturalism."
However his is a view not shared by Victorian Senator James Paterson, who is a member of the Australian Human Rights Committee.
"We have already seen how (18C) in its current, narrow way has restricted people's freedom of speech. This would further hamper it and would be a backwards step."
He disagrees that religion and culture fall under the same umbrella.
"People can choose religion and opt in and out and that's a good and healthy thing, but race is innate and is how you are born. Something you can change your mind on and enter in and out of should be under robust debate."
Under Tony Abbott, the federal government promised to change the controversial 18C by law, a decision since delayed indefinitely by the current Prime Minister Malcolm Turnbull.
"To be clear, the coalition has never had a position of entirely scrapping 18C. It has been revisited because after the QUT court case there have been a lot of people worried about the impact on free speech," Mr Paterson said.
In coming weeks, the Australian government will undertake an inquiry into the human rights act, and the 18C clause will once more hit the spotlight.
Senator Paterson says despite his reservations on including religion under the act, he is open to compromise.
"I think 18C definitely needs to be reformed and widen free speech not restrict it further... but one solution that has been put forward is to remove the words "offend or insult" from the clause, which could be something to consider," he said.
