Australia is set to hold the first same-sex marriage ceremonies on Dec. 7 since it was legalised in the Australian Capital Territory (ACT). Same-sex couples who are planning to get married in Australia on that day may grow frustrated when their unions will be declared invalid by the Australian High Court five days later.

Prime Minister Tony Abbott wants to declare the marriage equality legislation passed in ACT as unconstitutional. The High Court has previously reserved its judgment on the claim until Dec 12. Within the five-day window, there are 47 same-sex couples expecting to get married.

Australian Marriage Equality National Director Rodney Croome said unless the government can request an injunction, the marriages will push through. Mr Croome said the same-sex couples awaiting marriage know the issues and the risk that their union might be overturned by the High Court.

Mr Croome said Australians will see the unions on Dec 7 as not about the legality of gay marriage but about love and commitment to another person.

Australia lags behind countries, including Brazil, France, Canada, South Africa and New Zealand that have already legalised gay marriage.

Tony Abbott is a member of the Catholic Church with a lesbian sister. Mr Abbot said the ACT legislation contradicts Australia's Commonwealth Marriage Act. No state or territory in Australia allows gay marriage, but Tasmania recognises a same-sex marriage performed in other countries.

Attorney-General Simon Corbell said the ACT was surprised that the federal government had not sought an injunction to prevent gay marriages from taking place before Dec 12.

The Marriage Equality Act 2013 has been approved in the ACT Legislation Register. ACT Attorney-General Simon Corbell said he had signed the law to allow the act to take effect on Nov 7. He said same-sex couples who are planning to get married can do so by Dec 7.

The High Court will begin deciding on the eight legal questions on the act. The Commonwealth of Australia challenged the gay marriage law because it believes it is not in line with the federal Marriage Act. Federal Attorney-General George Brandis had insisted it is the only single law on marriage in the country.

The ACT will argue that states and territories can pass marriage laws for same-sex couples. Mr Brandis said he was looking to set the hearing at the earliest possible date to reduce any kind of stress that same-sex couples may experience if the Commonwealth succeeds in its plan to contest the law.