A legal challenge against the Australian Capital Territory’s same-sex marriage law will be heard in the country’s High Court less than a week before the first weddings are due to take place.

On Monday, Chief Justice Robert French said a two-day hearing by the full bench of the court would begin on 3 December.

ACT Attorney General Simon Corbell said the Marriage Equality (Same Sex) Act 2013 had been notified on the ACT Legislation Register and he had signed the instrument allowing the act to commence on Thursday this week.

“This means that the earliest date that marriages under this act could occur is December 8,” said Mr Corbell, reports the Sydney Morning Herald.

Equal marriage campaigners fear a legal challenge by the Federal Government could invalidate same-sex marriages performed after the law comes into force.

In October, the ACT became Australia’s first state to introduce marriage rights for same-sex couples.

Prime Minister Tony Abbott’s federal governing Liberal Party opposes equal marriage; the ACT’s Labor Government support the measure.

Last month, Mr Abbott warned same-sex couples against rushing to marry in the ACT until the legal challenge had concluded.

Mr Abbott said that the challenge was about upholding the Australian constitution and about preserving a “uniform approach throughout the commonwealth” to marriage laws.

Equal marriage remains banned at a federal level in Australia and efforts to legalise the measure failed in the Australian Parliament in September 2012.

Australian federal law was amended in 2004 to specify that marriage can only be between a man and a woman.