The High Court has agreed to hear a challenge to the Federal Government's same-sex marriage postal ballot on September 5 and 6, with a directions hearing to be held on Thursday.

The challenge will be heard a week before the postal vote is due to begin, with letters slated to be posted on September 12 to November 7, and the outcome to be announced on November 15.

Two separate parties applied for a temporary injunction preventing the postal vote but told a hearing this afternoon that they would be prepared to put their bid on hold given the case was being urgently heard.

In Melbourne, Federal independent MP Andrew Wilkie joined PFLAG (Parents and Friends of Lesbians and Gays) and Felicity Marlowe, who is raising three young children with her partner Sarah Marlowe, in challenging the case.

Represented by the Public Interest Advocacy Centre, they are arguing Finance Minister Mathias Cormann does not have the authority to appropriate funds for the postal vote.

They are also arguing that the Australian Bureau of Statistics has unconstitutionally been directed to seek an opinion rather than "statistical information".

Outside the court, Mr Wilkie said High Court Chief Justice Susan Kiefel's decision to hear the case before a full bench was a win for people in the community who had concerns about the non-binding, voluntary postal vote. Read more via ABC