The federal government’s same-sex marriage postal vote is lawful, the high court has found, clearing the way for the Australian Bureau of Statistics to send voting forms to 16 million Australians.

The seven high court judges unanimously dismissed the legal challenge mounted by Andrew Wilkie, PFlag (Parents, Family and Friends of Lesbians and Gays), and Melbourne lesbian mother Felicity Marlowe. The court also unanimously dismissed the case brought by senator Janet Rice and Australian Marriage Equality. The judges ordered the plaintiffs to pay costs.

The survey will be sent out from 12 September and the result announced on 15 November 2017, ministers George Brandis and Mathias Cormann said after the judgment was announced.

Brandis, the attorney general, and Cormann, special minister of state, said the government would “move swiftly” to enact new legislation adding additional safeguards to the postal survey process. That bill, seen by Labor and the Greens but not yet publicly released, would extend electoral law provisions on authorisations of ads and banning misleading information, fraud, bribery and intimidation to protect the survey.

However the Australian Electoral Commission’s chief legal officer, Paul Pirani, told a Senate committee on Thursday the ban on “misleading information” only applies to misrepresentations about the process of voting and the source of material, not its content. Those challenging the survey over two days of hearings at the high court in Melbourne argued the government acted inappropriately in allocating $122m to the ABS to conduct the vote; that the question of same-sex marriage is not within the scope of statistics collected by the ABS; and that it was wrong to ask people to sign up to the electoral roll for the vote because the issue could not be considered an electoral matter. Read more via the Guardian