Olympic swimming champion Ian Thorpe has joined the chorus opposing the Morrison government's proposed religious discrimination laws.

Thorpe will voice his concerns about the bill at Parliament House in Canberra on Thursday.

He's worried about its impact on women, people with disability and LGBTIQ people.

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The draft laws 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.

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."