Gay-rights advocates filed a court challenge on Thursday to the government’s unusual plan to canvass Australians’ opinion on gay marriage next month, while a retired judge said he would boycott the survey as unacceptable, labelling the vote “a novel, voluntary, non-binding, non-compulsory vote of a few citizens”.

Tasmanian independent federal MP Andrew Wilkie and marriage equality advocates Shelley Argent and Felicity Marlowe, applied to the High Court for an injunction that would prevent the so-called postal plebiscite from going ahead.

The mail ballot is not binding, but the conservative government won’t legislate the issue without it. If most Australians say “no,” the government won’t allow Parliament to consider lifting the nation’s ban on same-sex marriage.

Argent, the spokeswoman for the group Parents and Friends of Lesbians and Gays, said the non-compulsory postal vote was “designed to fail” by former prime minister Tony Abbott. “What they could do is have the free vote (in parliament) – there is more dignity and respect,” she said. “I am, as a mother, standing up and that is why we are going to the High Court.”

Gay-rights advocates and many lawmakers want Parliament to legislate marriage equality now without an opinion poll, which they see as an unjustifiable hurdle to reform. There were questions around whether the government can pay for the postal ballot without the parliament passing legislation.

“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 had legal advice that the postal ballot would withstand a court challenge. “I encourage every Australian to exercise their right to vote on this matter. It’s an important question.”

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. Kirby would not comment on the legality of the government proceeding with the 122 million Australian dollar ($96 million) ballot without Parliament’s approval, but said: “I’m not going to take any part in it whatsoever.”

“Mr Merkel feels that the idea of a postal vote running through the ABS may exceed the ABS’s authority, particularly when we consider whether a postal vote on marriage equality is statistic gathering or not,” Croome said.

Plebiscites in Australia are referendums that don’t deal with questions that change the constitution. Voting at referendums is compulsory to ensure a high voter turnout and that the legally-binding result reflects the wishes of a majority of Australians.

Pollster Martin O’Shannessy said a market researcher would be able to provide a more accurate picture of Australians’ attitudes toward gay marriage through telephone polling for less than $AU1.2 million.

Successive opinion polls show most Australians support gay marriage. But national referendums in Australia rarely change the status quo. Gay-rights advocates fear that on an issue that doesn’t directly affect most Australians, a majority might be persuaded to opt against change.

Acting Special Minister of State Mathias Cormann argued a public vote would be a “unifying moment for the country”, enabling those on the losing side of the argument to more readily accept the result. He rejected claims the debate around a plebiscite would be damaging, insisting the government trusted the Australian people to have a respectful debate.