The government has appointed Howard-era cabinet minister Philip Ruddock to lead a review into the legal protections for religious freedom in Australia, which has emerged as a contentious issue inside the Coalition ahead of the legalisation of same-sex marriage.

Announcing the review, Prime Minister Malcolm Turnbull said recent proposals for religious protections went beyond the immediate issue of marriage and warned any change should be undertaken carefully.

"There is a high risk of unintended consequences when Parliament attempts to legislate protections for basic rights and freedoms, such as freedom of religion. The government is particularly concerned to prevent uncertainties caused by generally worded Bill of Rights-style declarations," Mr Turnbull said.

Since the Australian people backed same-sex marriage in the postal survey, Coalition MPs have been pushing various proposals for religious exemptions, including allowing service providers to boycott weddings that conflict with their faith. One proposal would see a section of the International Covenant on Civil and Political Rights incorporated into the same-sex marriage bill.