The Bishop of South Sydney, Robert Forsyth, has recommended those who believe participation in a revised Marriage Act made them "unacceptably complicit with the change and the ideology" could cease their legal role in marriages if they wish.

"That question is, in the end, a matter for the individual conscience of each minister in consultation with their parish," he wrote.

The NSW Presbyterian Church has proposed the wholesale withdrawal from the Marriage Act if legalisation goes ahead.

But the Sydney Anglicans will not withdraw as a church, instead choosing to leave the decision to individuals.

The official sanctioning of same-sex marriage - a plebiscite is expected to be held in the next parliament - raises other issues, Bishop Forsyth said.

"There's a lot of concern," he told Fairfax Media. "Will religious freedom be changed?

"Would it be against the law for a person to refuse to engage in [gay weddings]?"

While he was confident Anglican clergy would not be compelled to officiate same-sex marriages, there were fears devout believers who worked as photographers, or who hired out halls for weddings, could be caught by anti-discrimination laws if they refused to provide their services to gay people.

This would amount to forcing "people to engage in effectively celebrating in same-sex marriage against their conscience", Bishop Forsyth, who is chair of the Sydney diocese religious freedom reference group, said.

Earlier this year the owners of a bakery in the US state of Oregon were ordered to pay almost $200,000 in damages after they refused to make a wedding cake for a lesbian couple.

Bishop Forsyth worries a similar fate could befall devout Australian Christians.

The Human Rights Commissioner, Tim Wilson, has convened a roundtable on religious freedom to be held in November. He has previously said that wedding service providers could be exempted from anti-discrimination laws to allow them to operate their businesses without compromising faith-based beliefs in heterosexual marriage.

Prior to any federal law changes, the issue of discrimination has already arisen. The Tasmanian Anti-Discrimination Commissioner is this week reportedly examining a complaint about a Catholic Church booklet opposing gay nuptials, on the grounds it may offend same-sex couples and their families.

Entitled Don't Mess with Marriage it was distributed by the church in Tasmania.

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