Many federal politicians who have spoken about the views of their constituents on gay marriage say they resent being told how to do their job.

MPs began reporting back to Parliament on Wednesday on the issue of same-sex marriage, after Greens MP Adam Bandt put forward a motion last year asking parliamentarians to consult their electorates.

The submissions come after the half-brother of independent federal MP Bob Katter spoke out against his sibling's criticism of gay marriage.

Last week Bob Katter said the idea of same-sex marriage deserved to be ridiculed, but Carl Katter, who is gay, told Channel Ten his sibling's views were damaging.

"It's an incredibly brave thing to do," Mr Bandt said.

"It highlighted the point that everyone had a brother, or a sister, or a son, or a daughter, or a relative, or a friend who was affected in some way by the discrimination that existed in Australian law.

"Why should not someone marry the person they love? I have great confidence that we will achieve full equality in the life of this Parliament."

Many of the Coalition MPs who spoke in Wednesday's debate said they were offended by the suggestion that they needed to be told to consult their constituents.

NSW Liberal MP Alby Schultz was the most outspoken.

"After 23 years in state and federal politics and a stint in local government, I am deeply offended at being told by the recently elected Member for Melbourne how to do my job," he said.

Mr Schultz and several of his Coalition colleagues said they received overwhelming feedback from their electorates for the Marriage Act to remain unchanged.

'Gutless step'

The LNP member for the Queensland seat of Dawson, George Christensen, said there is a lack of interest in his community about the issue.

"This is a motion that is a gutless step towards trying to change the law on marriage," he said.

Sorry, this audio has expired Gay marriage debate begins in Federal Parliament ( Naomi Woodley )

"It is a motion that says I haven't got the guts to put up a same-sex marriage bill because I know it will be defeated right now, so I'll just throw the concept out there so you will get used to it."

Coalition MPs were not the only ones to express their opposition to same-sex marriage.

Among others, Labor MPs Chris Hayes, Shayne Neumann and Mike Symon also reported overwhelming opposition to any change to the Marriage Act.

On the other hand, Labor MP Anthony Albanese said he is in favour of same-sex marriage but that "change is difficult".

There were some passionate contributions from other Labor MPs who say their constituents want change.

Queensland MP Graham Perrett said he has strong reasons for supporting same-sex marriage.

"Too many constituents told me their children were bullied and belittled because they were same-sex-attracted. Some were even driven to suicide," he said.

"I cannot sit idly by while the nation is complicit in this harm.

"It is time for this nation to protect committed monogamous relationships whatever the gender of the adults who wish to have their relationship recognised by the state."

In a statement, Bob Katter says he is proud of his half-brother, but still disagrees with his views on homosexual marriage.

Support for change

Newcastle-based Labor MP Sharon Grierson said she has long been a supporter of changing the Marriage Act.

"It's about the dignity of life, the dignity of love... it's an issue that goes to the core of the human experience - the need to be loved, love," she said.

Opposition communications spokesman Malcolm Turnbull said his survey showed 72 per cent of voters in his seat of Wentworth support same-sex marriage. He did not express his personal view.

Tasmanian independent MP Andrew Wilkie called on the Government to find a solution which would satisfy both sides of the debate.

"Many people in Denison feel strongly about marriage equality," he said.

'The Government needs to find a way to address this matter which recognises fundamental principles and represents both sides of the debate."

Other MPs reported support for civil unions but not same-sex marriage.