Challenge filed in court to Australian gay marriage ballot

Gay-rights advocates have lodged a High Court challenge to the government's unusual plan to canvass Australians' opinion on gay marriage next month, while a retired judge says he will boycott the survey.

Australians are to vote on gay marriage through a non-binding ballot by mail before the conservative government would consider legislating the issue. Lawyers lodged an application for a court injunction on Thursday that would prevent the so-called postal plebiscite from going ahead.

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

Prime Minister Malcolm Turnbull said the government had legal advice that the postal ballot would withstand legal challenge.