Conservative MPs believe up to 100 amendments are needed to a same-sex marriage Bill being proposed if the Yes vote succeeds, posing a major test for Prime Minister Malcolm Turnbull as he seeks to manage an emerging partyroom split.

With expectations growing that the Yes vote will be successful next month, conservative MPs are preparing a major reworking of a Bill proposed by WA senator Dean Smith that would have between 60 and 100 amendments put forward, sources say.

A group of conservative MPs are working on a revised Bill amid fears that moderates — including leader of government business Christopher Pyne — may rush through the Smith Bill without adequate partyroom debate.

Labor has indicated it will support the Bill, meaning the Government would easily have the numbers to pass the legislation through both Houses of Parliament.

Mr Pyne is understood to have angered colleagues in a meeting at Parliament House last week by suggesting legislation could pass in just two sitting days.

Tasmanian conservative senator Eric Abetz said the Smith Bill, which was based on the findings of a cross-party Senate committee, was “not acceptable as a starting point”.

“It (the Bill) is seriously inadequate, as parents, freedom of speech and religious freedom, along with conscientious objection, all need full protection,” Senator Abetz said, but he said this did not mean the No camp was conceding defeat.

Several other conservatives warned that Mr Turnbull would have a party-room revolt on his hands if he sought to expedite the passage of the Smith Bill.

“In the interest of party cohesion, I would suggest that approach would be incredibly ill-advised,” one said.

Another said the issue was “explosive” but was now just simmering under the surface, and warned that Mr Turnbull needed to protect parental rights and faith-based schools to keep the coalition base onside.

Senator Smith told The West Australian that his proposed Bill provided a “fair balance” to protect religious views.

“If there is a Yes vote, it will be necessary for the opponents of marriage to detail their amendments. This will provide a challenge to the Liberal Party because the community will not accept any winding back of Australia’s well-established anti-discrimination laws,” he said.