Labour has urged the government not "to drag its feet" over gay marriage as it hosted a meeting of religious figures who support legalising same-sex unions.
Representatives from the Quakers, the Unitarian Church and Jewish groups were among those at the event.
Labour says their backing shows a range of views among faith groups on the issue and not blanket opposition.
The government have offered a free vote on the issue amid criticism from the Church of England and some Tory MPs.
David Cameron, Nick Clegg and other senior ministers have long backed plans to change the law to allow civil marriage ceremonies for same-sex couples and legislation had been expected before 2015.
But the promise of a free vote in the Commons has led to claims the coalition is seeking to put the issue on the back-burner after several Conservative MPs said it should not be a priority for the government and threatened to reject the plans.
Labour says the debate should not be reduced to a battle between the Church of England and gay rights campaigners and the views of individuals and faith groups which support gay marriage must be respected as a matter of upholding religious freedom.
Paul Parker, the most senior figure in the Quakers, said his organisation believed there was "no difference" between a heterosexual marriage and a same-sex union since they demonstrated the same commitment between two individuals.
"We really do not acknowledge there is a distinction between two types of couples. We want everyone to have the same experience, both legally and on the day," he told BBC Radio 4's Today programme.
"We are calling for the law to catch up, really, with something we already recognise."
Civil partnerships, introduced in 2005, already give gay couples similar legal rights to married couples but Mr Parker said they were a "legal contract, not a spiritual one".
"There is a risk that people end up feeling that religious groups, en bloc, are against same-sex couples completely," he added.
"That is not the case. What we are seeing this as is an issue of religious freedom. We are not seeking to impose it on other religious groups who are not ready to do it or not willing to do it. But we do want that freedom to be able to do what we see as the right thing."
'Step too far'
Among Church of England clerics who attended were Dr Jeffrey John, one of the Church's most high profile gay figures and Lord Harries, the former Bishop of Oxford.
Church leaders have suggested the proposals - currently the subject of a consultation - would alter "the nature of marriage" and represent a real threat to the established Church's status in society.
Although ministers say the ban on same-sex couples marrying in a religious service will remain in force, the Church of England fears this could be challenged in European courts.
Canon Chris Sugden, executive secretary of Anglican Mainstream, said he believed that same-sex marriage was a "step too far" and not compatible with Christian teachings.
"The issue is whether same-sex relationships, in the Christian understanding, are on the same level as heterosexual marriage," he told the Today programme.
"And it is very clear from the Christian scriptures that we are committed to that they are not."
He stressed his opposition was on social as well as religious grounds.
"Marriage bonds together a man and a woman and their children and is a building block for family and for society," he added.
Shadow home secretary Yvette Cooper, who hosted Wednesday's roundtable, has said there are "serious contradictions" in the government's position.
She has said any religion or faith group wishing to conduct same-sex marriages on their premises should not be prevented from doing so and legislation should be brought forward this year.