From the Rudds to the Bolts, an issue that divides the nation also divides families.

This morning, Foreign Affairs Minister Kevin Rudd's sister Loree Rudd said she quit the Australian Labor Party last week in protest at its policy shift from opposing to supporting gay marriage after the national Labor Party Conference.

"I no longer liked the direction the Labor Party was going at state or federal level and I couldn't work for a party that had endorsed homosexuals marrying," she said.

Later, Stephanie Bolt, sister of right-wing Herald Sun blogger Andrew Bolt came out in defence of gay marriage on the Crikey website after she left a comment on his blog that was not published.

Ms Bolt said she was a lesbian who was married to her partner under Canadian law.

"It may seem naive, but having that certificate in my hand made me untouchable, secure, normal, and for those wonderful few weeks, I could drop the shield," she said. "It's disappointing beyond measure that my brother and others who share his views don't wish that for me and everyone else like me."

Ms Bolt said she had "received respect and love from people important to me as I made those first tentative steps out of the closet," but had also been "verbally abused" and "chased down city streets" by others because of her sexuality.

"Homosexuals should be loved and treated right and they should not be discriminated against.

"It is a horrible thing for them to be discriminated against and that's why my brother introduced laws so they are not discriminated against.

"But to make that huge leap from their rights to breaking a commandment of Moses, to say homosexuals' relationships is marriage, is utter nonsense."

Ms Rudd said when she entered a polling booth at the next federal election, she would not vote for Labor unless the party had changed its policy on gay marriage.

She would look at other candidates, including those from Katter's Australian Party, and would make her decision based on the integrity of the candidate.