Australia is preparing to ask citizens whether the country should legalize same-sex marriage, but there are deep divisions within the country and a legal hurdle.

The Australian government's attempts to call a referendum on the issue failed in the Senate, so it has opted for a plebiscite, in the form of a mail-in ballot.

The government is not calling it a vote or referendum, because it's non-binding, and instead is calling it a survey.

Gay-rights advocates and many legislators are opposed to the idea of a plebiscite, saying it will only fuel a vitriolic and homophobic campaign.

Critics say parliament should vote on the matter without an opinion poll, which they see as an unjustifiable hurdle to reform.

Lawyers for independent legislator Andrew Wilkie and marriage equality advocates Shelley Argent and Felicity Marlowe, applied to the High Court for an injunction last week to prevent the postal plebiscite from going ahead on constitutional grounds.

"We will be arguing that by going ahead without the authorization of parliament, the government is acting beyond its power," lawyer Jonathon Hunyor said.

Prime Minister Malcolm Turnbull said the government obtained legal advice that the ballot would withstand a court challenge.

Retired High Court judge Michael Kirby, a gay man who supports marriage equality, dismissed the ballot as "irregular and unscientific polling."

"It's just something we've never done in our constitutional arrangements of Australia, and it really is unacceptable," Kirby told Australian Broadcasting Corp.

The high court will hear challenges to the survey next month, before ballots are due to be distributed to Australian homes. The government wants to begin the mail-out on Sept. 12.

If the survey survives the court challenge, the results will be announced on Nov. 15.

It's estimated the ballot will cost $122 million Australian dollars ($123 million Cdn).

With files from Reuters