Malcolm Turnbull has introduced the Plebiscite (Same-Sex Marriage) Bill 2016 into the federal Parliament. The bill has been overshadowed by the debate over whether a plebiscite is desirable in the first place. Unfortunately for the Prime Minister, his bill strengthens the case of those who reject the national vote. It is flawed in key respects, and could be challenged in the High Court.

The plebiscite bill proposes that Australians be asked a simple question: "Should the law be changed to allow same-sex couples to marry?" This is the wrong question. It fails to capture the full extent of how the marriage act would be changed.

PM introduces plebiscite bill to parliament

Malcolm Turnbull spoke of the societal benefit of more marriages in Australia while introducing the contentious same-sex marriage plebiscite bill on Wednesday.

Many bills have been introduced into the federal Parliament to bring about same-sex marriage. These typically extend marriage rights not only to same-sex couples, but also to intersex people. The wider change is needed because same-sex marriage does not necessarily encompass people unable to identify as being either male or female.

An example is the Marriage Legislation Amendment Bill 2015, sponsored by a cross-party group of MPs including Coalition member Warren Entsch. It sought "to allow couples to marry, and to have their marriages recognised, regardless of sex, sexual orientation, gender identity or intersex status". It went beyond the proposed plebiscite question in defining marriage not in terms of heterosexual or same-sex relationships, but as "the union of two people to the exclusion of all others, voluntarily entered into for life".

The poor fit between the plebiscite question and the legal change could be a significant problem. Even an overwhelming yes vote could give rise to suggestions that Australians have not provided a mandate for altering the marriage act beyond recognising same-sex marriage. If the plebiscite question were implemented faithfully, intersex people would remain subject to discrimination.

This exposes an even larger issue. The government says that its plebiscite bill is sound because it adopts the same, well-travelled path as referendums to change the constitution. This is not true in several respects, including in ways that undermine the viability of the plebiscite.

When people vote in a referendum, they do so in full knowledge of how the law will be changed. Every referendum is accompanied by the specific, word by word, changes to the constitution. As a result, there can be no doubt about what Australians are voting for.

By contrast, the plebiscite bill fails to set out how the marriage act might be changed in the event of a yes vote. People would vote on the general concept of same-sex marriage without being provided with the full details, including as to several divisive issues. This uncertainty could be exploited by the No campaign.

These unresolved questions extend beyond the position of intersex people to whether the law should clarify that religious ministers would not be bound to solemnise a marriage. Another point of contention is whether the marriage act should permit commercial operators to refuse to supply goods and services in respect of same-sex marriages due to a religious objection.

A further departure from referendum procedure is the proposal that $15 million be provided to taxpayer-funded Yes and No campaigns. The government has made much of the fact that the 1999 referendum on the republic allocated funding to the Yes and No cases. This is correct, but it is the exception. Instead, the normal rule as clearly stated in the federal law that governs referendums is that: "The Commonwealth shall not expend money in respect of the presentation of the argument in favour of, or the argument against, a referendum proposal."

The final difference relates to the consequences of a Yes vote. A Yes vote in a referendum produces a change to the constitution without further parliamentary debate. On the other hand, it is not proposed that the plebiscite produce any outcome. Instead, Parliament would be left to interpret the result. This undermines the value of holding the vote, and could prove fraught in light of uncertainties with what Australians have voted to support.

Each of these problems can be fixed by amending the government's plebiscite bill. However, even if this does occur, further obstacles remain. These include the possibility of a High Court challenge. The constitution authorises the holding of a referendum, but makes no mention of a plebiscite. This means that the legal basis for the poll is uncertain.

It is likely that the High Court would uphold the plebiscite on the basis that it falls under the federal Parliament's marriage power. On the other hand, specific provisions of the bill, such as those for compulsory voting, and the funding of the Yes and No cases, may prove vulnerable. Even if the Prime Minister somehow convinces Parliament to pass his bill, he might yet find his plebiscite derailed.

Professor George Williams is Dean of Law at UNSW.

This opinion piece was first published in The Sydney Morning Herald.

George Williams