A parliamentary committee has outlined its support for the human rights goals in a private members bill to legalise same-sex marriage, but some of its members have penned a dissenting view.

Key points: Report says bill would promote equality and end discrimination under Marriage Act

Report says bill would promote equality and end discrimination under Marriage Act Three members say the bill breaches rights to freedom of religion

Three members say the bill breaches rights to freedom of religion Greens say the criticisms are "bizarre" and "clutching at straws"

The Parliamentary Joint Committee on Human Rights examines human rights issues in pieces of legislation.

Its wide-ranging report released on Tuesday did not endorse a bill put forward by Liberal National MP Warren Entsch to legalise same-sex marriage, but did find it would work to promote equality and end discrimination under the Marriage Act.

The report also noted the legislation would likely promote the right to respect for the family by "extending the availability of marriage to same-sex couples", and that the bill "does not limit, and may promote, the obligation to consider the best interests of the child".

But it is rights to freedom of religion that led three members of the committee to present a different view.

Nationals senator Matt Canavan, Nationals MP David Gillespie and Liberal MP Michael Sukkar said the bill would breach the human rights of civil marriage celebrants.

"It's important to recognise this report is about the human rights implications of the bill, not whether any individual members or senators support the bill," Senator Canavan said.

"We have concerns that the bill as drafted does not protect peoples' freedom of religion and belief.

"Those rights are held with individuals, not with the Catholic Church, or Islam, or a Buddhist Temple."

Senator Canavan said the bill was not in line with key United Nations conventions.

"The way the bill is drafted, only ministers of religion are exempt, not celebrants, and not even ministers of religion who may have a different view to the religious practice that they're accredited under," he said.

"Any change to our marriage laws should ensure that every Australian has the right not to solemnise same-sex marriages, if they're in the game of being a celebrant and solemnising marriages.

"There are other bills drafted in the Parliament that extend an exemption to celebrants, not just ministers of religion, and we think the bill would be much more in accord with our international human rights obligations if it took that path."

The trio's concerns went further than just rights to religious freedom, arguing that it breaches rights in regards to families and children.

Criticisms of bill are 'clutching at straws', advocates say

One of the cross-party bill's co-sponsors, Labor MP Terri Butler, hit out at suggestions celebrants' rights were at risk.

"When you're talking about this bill, you're talking about human rights. We're actually saying that people should not be prevented from marrying because of their sexuality," she said.

"To suggest that somehow curing that discrimination is somehow a human rights breach is living in a parallel universe."

Ms Butler said while religious practitioners were exempt from performing same-sex marriages, the exemptions should not extend to private sector workers like civil celebrants.

"Our bill makes it very clear that religious ministers, chaplains, clergy, are not required to undertake marriage ceremonies for same-sex couples," she said.

"To start going out to the private sector and saying, 'well, if you have a particular religious belief, you can refuse to marry people of the same sex' ... is not just silly, it's also inconsistent with the way the discrimination law has worked for decades."

The bill is unlikely to come to a vote on the floor of Parliament, but regardless of that the dissenting report has raised the ire of the Greens.

"This is just the latest last-ditch effort for opponents of marriage equality in this Parliament to delay reform, and this time they're cloaking their bigotry and homophobia in the language of human rights and some of the claims that are made are insulting in the extreme," Greens senator Rob Simms said.

"The suggestion that somehow same-sex parents are deficient or failing to meet the needs of children is incredibly insulting.

"It's incredibly insulting to gay and lesbian people and same-sex parents, but it's also insulting to their friends and family right across the community."

Senator Simms described the views as "clutching at straws".

"All of the legislation that's been before the Parliament in recent years has dealt with the issue of religious organisations performing marriages, and said that that isn't binding on religious organisations," Senator Simms said.

"When it's civil marriage, then of course the state has a right to step in, we're recognising religious freedom but at the same time recognising that under federal law all people should have an opportunity to marry.

"The great irony here is that the United Nations has been a big advocate for recognising equality for LGBTI people — to use the Charter of Human Rights to try and justify homophobia and bigotry is bizarre and insulting."