Same-sex marriage opponents officially launch 'no' campaign

The campaign against same-sex marriage has held its national launch in Sydney, with prominent federal politicians Corey Bernardi and Matt Canavan taking the podium to champion the no vote.

About 500 people, many with shirts and placards bearing the slogan "It's ok to say 'no'", filled the International Conference Centre at Darling Harbour tonight.

The Coalition for Marriage, the group at the centre of the campaign headed up by Australian Christian Lobby chief Lyle Shelton, placed the focus on the flow-on effects of altering marriage.

Senator Bernardi, who received a standing ovation, warned the audience of "weaponised" anti-discrimination laws and "legal warfare" against supporters of traditional marriage if the Marriage Act is changed to include same-sex couples.

"You can imagine the barrage of abuse and insults because you're starting to question what they're taught in schools, or because you dare not to recognise a couple as a married couple because they happen to be of the same gender," he said.