People from both sides of the debate crowded into the Sir Raymond Ferrall Centre at the University of Tasmania's Newnham campus, sitting in the aisles and lining the walls of the lecture theatre to hear three speakers offer a defence of the Marriage Act.

Separately organised by Tasmanian Young Labor with Rainbow Labor and the Tasmanian University Union with the Tasmanian Gay and Lesbian Rights group, about 40 protesters held up placards saying "It's about equality", and "I don't mind if you're straight, just don't flaunt it in public" outside the centre before joining the two-hour meeting.

The Save Marriage meeting was held to field grassroots opposition to potential changes to the act, which will be discussed at the Labor Party national conference later this year. The act has defined marriage as between a man and a woman since 2004.

Tasmanian Liberal senator Guy Barnett campaigned to have the current definition enshrined in law and spoke in its defence at the meeting. "I believe it's a bedrock institution that has served our nation well," Senator Barnett said.

Tasmanian Young Labor spokesman Adam Clarke said the protesters attended the meeting to peacefully offer an opposing view. "We think that everybody should have equal rights under the law and equal rights to the law, and that's the view we will be trying to put forward," Mr Clarke said.