Labor frontbencher Tony Burke has called for an investigation.Credit:Michelle Smith
Mr Burke,said his western Sydney electorate of Watson was out of step with national opinion in that it did not support change,and he had reflected this sentiment by voting against same-sex marriage in 2012.
But Labor's finance spokesman said the debate on same-sex marriage was becoming"harsher and angrier"and would only become more divisive.
"We need to get to the next stage of the conversation to explain why those who do not want the change will be unaffected by it."
Same-sex marriage advocates welcomed Mr Burke's change of heart,which they estimated would bring them within three votes of majority support for the change in the house of representatives if Liberal MPs were granted a free vote. Campaigners believe there is a slim majority in support of same-sex marriage in the Senate.
Prime Minister Tony Abbott on Sunday ruled out Australia following Ireland's example and settling the issue by a popular vote,saying it was a matter for parliament to decide.
Mr Abbott acknowledged the issue was important to millions of Australians,but said his immediate priority was boosting small business confidence through measures announced in thebudget.