We're in it to win it: equality advocates

Equality advocates say they have a duty of care and a responsibility to campaign for same-sex marriage despite opposing a postal ballot in the High Court.

Equality advocates have officially announced they'll campaign for a Yes vote in the upcoming postal survey on same-sex marriage.

The Equality Campaign spokesman Tiernan Brady says advocates are still opposed to the voluntary plebiscite but if it goes ahead "we are in this to win this".

"Our call today is to enrol and check your address - you need your voice to be heard if we have to go down this road," Mr Brady said in Sydney flanked by other campaigners including NSW MP Alex Greenwich from Australian Marriage Equality.

The Equality Campaign is a joint initiative between Australian Marriage Equality and Australians For Equality.

The nationwide campaign was launched 12 months ago in the hope of securing a parliamentary vote on marriage equality.

Mr Greenwich said marriage equality supporters had been let down by the government and efforts needed to be doubled to achieve a fair outcome.

"We must make sure today and tomorrow we tell as many people as possible to enrol to vote, that is the one critical thing that supporters of marriage equality can do."

Activist group GetUp revealed earlier on Friday it would work with marriage equality groups to run a "powerful grassroots campaign" advocating for a Yes vote while also supporting a High Court challenge against the postal survey.

Campaigners headed to the High Court on Friday afternoon in an attempt to stop the planned plebiscite.

Chief Justice Susan Kiefel in Sydney said the full bench would hear the case in early September.