Plaintiff James Obergefell plays with his ring outside the US Supreme Court on April 28, 2015 in Washington, DC. Source: AFP

“I think we should [be allowed a conscience vote],” he told Sky News.

“I think you’ll get a truer test of the feeling within the Parliament if both the big parties of politics, the Coalition [and] the Labor Party do have a conscience vote.

“I think that will make for a more interesting debate and a truer test of the feeling within the Parliament on this subject.”

The issue is back in the spotlight after Deputy Labor leader Tanya Plibersek called on her party to impose a binding vote on its federal MPs.

Currently, the Labor Party supports same-sex marriage but it is not compulsory for its members to support it in a vote.

A binding vote would change this agreement so all Labor MPs would have to support the campaign.

“This is an issue about legal equality, and marriage of course for some people is a religious sacrament but for many, many people it is, as well as that or indeed instead of that, it is a legal agreement, it’s an acknowledgment by our community of the rights and responsibilities that a permanent relationship presents and I think when you talk about an issue like this, which is an issue of legal discrimination it is important for the Labor Party to say, ‘We don’t agree with legal discrimination,’ Ms Plibersek told ABC Radio on Monday.

While Mr Sinodinos has supported marriage equality in the past, the issue has slowly dropped out of mainstream politics.

Tanya Plibersek believes Labor MPs should follow the party line and support gay marriage. Source: News Corp Australia

In support: Senator Arthur Sinodinos. Picture: Jeremy Piper Source: Supplied

Liberal Democrat Senator David Leyonhjelm, who introduced a same-sex marriage bill to Parliament last December, told reporters the Prime Minister was “not enthusiastic” about it, according to Fairfax.

“His argument was the government’s got plenty of troubles without this one coming along.

“He would prefer I didn’t [introduce the bill].”

While Australia continues to fall behind on the issue, the US steams forward as its Supreme Court weighs a potentially historic decision that could see gay marriage legalised nationwide.

So far, 36 of the 50 states allow same-sex marriage, along with the District of Columbia.

The US Supreme Court heard two and a half hours of arguments about the same-sex marriage ban in Kentucky, Michigan, Ohio, and Tennessee. Picture: Johnny Bivera Source: AFP

An Ultra-Orthodox Jew shouts anti same-sex marriages slogans outside the US Supreme Court. Picture: Mladen Antonov Source: AFP

US Senator Cory Booker gives the thumbs up to the crowd as he exits the Supreme Court. Picture: Drew Angerer Source: AFP

The Court, consisting of nine Justices, appeared divided on whether same-sex couples have the constitutional right to wed.

Justice Anthony Kennedy, who appears to be the swing vote in the case, worried about changing the definition of marriage from the union of a man and a woman, a meaning that he said has existed for “millennia-plus time.”

“It’s very difficult for the court to say ‘We know better”’ after barely a decade of experience with same-sex marriage in the United States, Kennedy told Mary Bonauto, a lawyer representing same-sex couples.

The court heard from plaintiffs from four states — Ohio, Michigan, Tennessee and Kentucky — where gay marriage is still barred.

“In a world where gay and lesbians live openly as our neighbours, it’s simply untenable that they should be denied, or that they should wait,” Solicitor General Donald Verrilli, a top Obama administration lawyer argued in support of the plaintiffs.

“They deserve the equal protection of the law, and they deserve it now.”

Married with pride: A couple poses for a photo near the Supreme Court in Washington, DC. Picture: Drew Angerer Source: AFP

People cheer as the legal teams, defending same-sex marriages leave the US Supreme Court on April 28, 2014 in Washington, DC. Picture: Mladen Antonov Source: AFP

Plaintiff Rev. Maurice Blanchard, of Louisville, Kentucky, makes heart with his hands. Picture: Cliff Owen Source: AP

A gay couple pose with their child outside the US Supreme Court. Picture: Picture: Mladen Antonov Source: AFP

Supported by the Obama administration, the 16 plaintiffs want their marriages to be recognised as constitutionally protected in all US states.

Their home states currently define marriage as being between a man and a woman, and do not recognise gay marriages carried out elsewhere in the country.

If the Supreme Court were to rule in favour of the plaintiffs, it would thus make a de facto decision against all 13 states banning gay marriage.

Experts say recognition of same-sex marriage seems inevitable.

The Justices will meet in private on Friday to take a preliminary vote on the issues and assign opinions.

Only time will tell if Australia follows suit.