Banning same-sex marriages may not be valid under the constitution

Making marriage the exclusive domain of couples comprising a man and a woman might be more difficult than Prime Minister John Howard imagines. He indicated the intention of his government to do just that.

"The proposal simply would be to insert a definition in the Marriage Act which gives formal expression to what most people regard to be the case and that is marriage as we understand it in Australia is between a man and woman," he told Paul Murray on Radio 6PR on April 27. "This is not directed at gay people. It's just directed at reaffirming a bedrock understanding of our society."

But it is not so simple. It is a legal, constitutional and political minefield.

Marriage is not generally defined in the Marriage Act 1961. Everyone just assumed it was the union of a man and a woman. Marriage is only referred to only once in the Act as the union of a man and a woman. And that is in the form of words that a civil celebrant must use at the ceremony. But that has no legal bearing on the sex of the couple taking part in the ceremony.

Throughout the Act, those getting married are referred to as "parties" or sometimes as a "person".

It means, perhaps, that a celebrant (presumably) civil could "marry" two men or two women. Such a union would undoubtedly be challenged in the Family Court, probably by the Attorney-General. The outcome would be anyone's guess.

Another possibility for testing the legality of gay marriages lies in the recognition of foreign marriages.

Broadly, Australian law recognises foreign marriages. People married overseas do not have to remarry in Australia before all the rights and obligations of marriage flow to them - various social welfare rights and access to the Family Court to determine disputes over their children and property. But, again, in defining which foreign marriages will be recognised, no-one to put in any definition that the only foreign marriages to be recognised would be those between a man and a woman.

Recently, the Netherlands, Belgium, several Canadian states and two US states have recognised gay marriages. A gay couple (Australian or foreign) who married in these jurisdictions could move back to Australia and seek a declaration in the Family Court that they are married for the purposes of Australian law. Apparently, some couples are lining up to do precisely this. The Marriage Act says Australia recognises "every marriage solemnised ... in a foreign country where under the local law, the marriage was, at the time it was solemnised, recognised as valid" - like one of those gay marriages in Canada, for example.

If the Family Court declared a gay marriage valid, the couple would have all the rights and duties of married people. This is the difference between "marriage" and contractual obligations that a gay couple might enter in to. The former is status-changing and forever binding; you can contract out of the latter.

So Howard has to do more than insert a simple definition in the Marriage Act. He has to also change the provisions about the recognition of foreign marriages in the Marriage Act and the Family Law Act. More snags. Constitutionally, it is easier to do the latter than the former.

A law refusing to recognise foreign marriages would come under the Commonwealth's external affairs power.