The sister of Tony Abbott, the Prime Minister of Australia, has said he may be “shifting” his stance on equal marriage, despite conceding that he may never vote in favour of it.

Openly gay Christine Forster, a Liberal councillor spoke at an Australian Marriage Equality forum on Wednesday to say that although Abbott remains “comfortably opposed” to equal marriage, he understands the importance of the issue across the world.

“He’s increasingly aware of how important this issue is to members of his family, to me – his sister, to his daughters, and to the rest of the world,” she said.

Continuing, however, she said she was unsure on whether he would ever change his view.

“His view, for whatever reason he holds it, is his view and he’s entitled to his view… But he hears me, he hears us.”

The National Secretary of the Australian Workers’ Union, Paul Howes, earlier today said he wants Labor MPs to be forced to vote in favour of equal marriage, in line with the party’s platform.

Currently, Labor MPs would be allowed a conscience vote on the issue.

The party lost power in September’s federal election. Former Labor leader and Prime Minister Kevin Rudd, who supports equal marriage, lost out to conservative challenger Tony Abbott, who opposes marriage rights for same-sex couples.

Former Australian Prime Minister Julia Gillard earlier this week made her first public appearance since being ousted as Prime Minister in June, and when asked, blamed her opposition to equal marriage on her 1980s feminist politics.

Efforts to legalise the measure failed in the Australian Parliament in September 2012.