The government plans to introduce laws to prohibit discrimination on the grounds of religious beliefs but opponents to the bill believe it will open the door for people to discriminate against marginalised groups under guise of religion.

Mr Thorpe, who was a loud voice in the push for marriage equality, was joined in Canberra by Anna Brown, chief executive of Equality Australia.

"I believe in an Australia that has a sense of a fair go, this bill most certainly doesn't do that," Mr Thorpe said.

The bill would allow people to be discriminated against on the basis of their age or gender, he said.

"It will also restrict peoples' ability and access to be able to use our hospital services, our schools, and it goes further, it will have a huge impact on the LGBTI community in particular."

The government is now in consultation over the second draft of the laws, but Mr Thorpe and Ms Brown said it should not proceed at all.

"It is something that we'd be prepared to work on, but I think at this stage my preference would be this was scrapped," Mr Thorpe said.

Former High Court justice Michael Kirby has also spoken out against the bill.

Mr Kirby, who is backing a new campaign against the bill called #DontDivideUs, believes all Australians could be worse off under the bill.

"This is not a bill that protects Australians from discrimination on religious grounds. Instead, it actively facilitates intolerance and will work to divide rather than unite Australians," he said in a statement.

"The government should heed the chorus of opposition to this law and abandon this ill-considered measure."

The draft laws - yet to be put to parliament - are aimed at protecting people of faith from discrimination. The proposal would allow hospitals to hire on religious grounds and give doctors the ability to reject procedures on the same basis.

Business and union groups have this week urged the government to amend the proposal, saying the bill could harm employees.

Ms Brown said the bill was friendless, with opposition to the legal changes growing every day.

"This bill is deeply flawed and will take us backwards."

Conservative Liberal senator Concetta Fierravanti-Wells has also spoken out against the proposal, saying no bill would be better than the government's "flawed bill".

The government has said the aim of the laws is to make protect Australians who are denied jobs or services on the basis of their religion or lack of religion, and to allow people to express their beliefs without the prospect of "law-fare".

But opponents are particularly concerned with clauses that would mean people could use the bill to make statements of belief that could be discriminatory against others.