OPPOSITION Leader Tony Abbott says the federal election shouldn't be muddied by a referendum on same-sex marriage.

Key independent Tony Windsor on Monday reignited the same-sex marriage debate after backing the idea of a plebiscite on September 14.

Mr Windsor said it could be an opportunity to resolve the issue, but he wouldn't be leading a push for a vote later in the year.

With New Zealand and then France legalising same-sex marriage in recent weeks, attention has again turned to Australia's response after federal MPs have voted down similar legislation.

Mr Abbott said the federal election should be "uncomplicated by other matters".

"I think the government and now the independents will want to muddy the waters with other things, but the election in September should be a referendum on the carbon tax. It should be a referendum on the current government," he said during a break in the annual Pollie Pedal in South Australia.

Finance Minister Penny Wong, who is in a same-sex relationship, said she would "sound a note of caution" about the idea of a plebiscite because it would be a "very high bar to jump".

Senator Wong pointed to the 1999 referendum on whether Australia should become a republic, which failed in all states despite the issue having strong public support.

"My view is the parliament has a responsibility and will one day discharge that responsibility," she told Sky News.

Conservative NSW state MP and Christian Democrats Leader Fred Nile, supports a vote on same-sex marriage because he thinks a majority would reject it.

"The information that I get when I'm travelling around is that there's no support for same-sex marriage," he told AAP.

Australian Marriage Equality national convener Rodney Croome feared a plebiscite would divide the electorate.

"We fear cashed-up opponents of marriage equality would exploit a referendum to polarise the electorate and demonise gay and lesbian people in a way that will impact badly, particularly on young gay people," he said in a statement.

Australian Greens leader Christine Milne said a referendum would be a distraction and the real stumbling block was Mr Abbott decision's not to allow opposition MPs a conscience vote on the issue.

However, independent Senator Nick Xenophon said it could be a way to break the impasse.

"When you've got a vexed, intractable issue, sometimes a referendum ... might be a way to cut through the issue," he told the Seven Network.

Originally published as Marriage vote will complicate poll: Abbott