On 12 August last year at a coalition meeting in Parliament House that Education Minister Pyne said could be likened to a stacked party branch meeting, 66 MPs decided that there has to be a plebiscite to decide the marriage equality issue.

That is 66 out of a total of 226 members of parliament, about 30%.

Financial costs of a plebiscite have been estimated to be between $160 and $500 million dollars and the emotional cost to people personally affected will be great.

Several coalition MPs have since stated that they will not change their vote on the eventual bill even if the majority of Australians vote for changes.