The coalition has failed to have a statement affirming the importance of marriage included in a bill that's removing commonwealth law discrimination against same-sex couples and their children.
The bill has passed the lower house, with the government voting down the amendment proposed by opposition justice spokeswoman Sussan Ley.
Attorney-General Robert McClelland highlighted Opposition Leader Malcolm Turnbull's absence from the debate, urging him to retain his commitment to removing discrimination against same-sex couples.
"I note ... (he) has previously expressed support for removing discrimination against same-sex couples and I accept his genuineness in that, Mr McClelland told parliament.
"Indeed, prior to the last election, he pledged to continue the fight until justice is done.
"In that context, I was a bit disappointed that the Liberal leader did not see this bill as being important enough for him to participate in the debate in the chamber to support the fundamentals of the legislation and to counter some of the more extreme views that some of his colleagues expressed during the debate."
Mr McClelland said he was disappointed with comments by Liberal MPs Stuart Robert and Bronwyn Bishop, that the reforms undermined the institution of marriage.
"With respect to those members they are simply wrong," he said.
"It was perhaps disappointing that they went further to suggest that far from removing discrimination against same-sex couples, we should be discriminating in favour of married couples."
The bill will amend 68 Commonwealth laws to remove same-sex discrimination in a range of areas including discrimination against children of same-sex couples.
The Same-Sex Relationships Bill (Equal Treatment in Commonwealth Laws-General Law Reform) Bill 2008 will now proceed to the Senate.
The opposition has referred the bill to the Senate's legal and constitutional affairs committee, which will report by September 30.
It is concerned that the bill may have the unintended consequence of the recognition of same-sex marriage.
