Mr Broad said in October that would withdraw his support for the government if it tried to bring about same-sex marriage by any mechanism other than the plebiscite.

“The government that I am a part of and will remain a part of is conditional on the fact that the only way that there will be a change to the Marriage Act in this parliament is a plebiscite,” Mr Broad said previously.

Mr Broad later qualified his comments and said he would guarantee his budget supply vote to the government if he moved to the crossbench.

Sky News reported on Thursday morning that Mr Broad’s colleagues were worried that we could carry out his threat from last year.

Several Liberal lower house members have indicated that they were prepared to cross the floor and vote with the opposition in order to force debate on a bill legalising same-sex marriage.

If the bill passes the lower house, it will likely pass the senate as well.

Liberal members and senators are due to hold a meeting on Monday at 4pm, where a secret ballot will likely determine the party’s policy on same-sex marriage.

The most widely predicted results would be support for a non-compulsory, non-binding postal plebiscite but this option would likely face a challenge in the High Court on constitutional grounds.

Mr Broad did not respond last week to requests for comment from the Stawell Times-News, Sydney Morning Herald and other national media organisations.

On Monday, Mr Broad confirmed the Sky News story.

“If the Liberals come out with a conscience vote, then yeah, I don't make idle threats," Mr Broad told The Sunraysia Daily.

Mr Broad said he would not be the only member to quit the government’s ranks.

“It won't be me only, the whole show would blow up,” he said.

Prime Minister Malcolm Turnbull and the Coalition would be reduced to a minority government if Mr Broad quit the government but maintained a vote of confidence and budget supply.

Sky News stated Mr Broad had told National Party colleague he will maintain his threat and had discussed the issue with party leader Barnaby Joyce later on Thursday.

After Mr Broad made his original threat, Mr Joyce criticised the decision via a Radio National interview.

“I said, as you would expect, ‘that is not helpful’,” Mr Joyce said.

“I clearly said this is not the preferable way to do business.

“I’m not going to go into every word I said but, quite obviously, any person in parliament making a statement that they’re going to bring down the government, I don’t think the Australian people want that.”

If a plebiscite, a non-legally binding referendum, is held, Mr Broad has previously stated he will vote for or against same-sex marriage based on the result from the Mallee electorate.

Member for Wannon Dan Tehan has pledged to vote in line with any national result.

Mr Tehan confirmed on Monday afternoon that he supported holding a plebiscite on same-sex marriage.

“What I said to the electors of Wannon before the last election was I supported a plebiscite and that I would respect the outcome of that plebiscite,” he said.

“Having made that clear commitment to the people of Wannon, I will be honouring that commitment.”

The government has considered holding the plebiscite via postal ballot rather than an election-style vote.