Last week, the Home Office launched a 12-week public consultation on gay marriage.
The proposals, which would allow partners to have a civil wedding and take the same vows and commitments as opposite sex couples, have faced fierce opposition from both church leaders and a minority of members of the Conservative Party.
Now the Muslim Council of Britain (MCB) has waded into the debate, telling The Telegraph that 'redefining' marriage is 'unnecessary and unhelpful'.
'With the advent of civil partnerships, both homosexual and heterosexual couples now have equal rights in the eyes of the law,' said Farooq Murad, secretary general of the MCB.
'Therefore, in our view, the case to change the definition of marriage, as accepted throughout time and across cultures, is strikingly weak.'
He added that gay unions are not accepted by Islam.
Lord Singh, head of the UK's Network of Sikh Organisations, has also condemned the proposal, calling it a 'sideways assault on religion'.
'It is an attempt by a vocal, secular minority to attack religion,' he told BBC Radio 4’s Today program.
The Home Office's consultation paper, which proposes to allow gay couples to marry in a registry office and give those already in a civil partnership the option to convert it into a marriage, has been slammed by members of the Anglican and Catholic churches.
Catholics were also urged to oppose gay marriage during masses on 11 March in a letter written by the Archbishop of Westminster, calling Christians to protect the meaning of marriage.
Not all Christian groups are opposed to gay marriage, with the Quaker church saying they support same-sex unions.
However, equality campaigner Peter Tatchell criticized the proposals for still barring religions from hosting weddings, even if they want to.
The Trade Union Congress (TUC) has welcomed the government’s consultation, saying it is an important step toward LGBT equality, but agrees that the law should go further and allow religious weddings.
TUC General Secretary Brendan Barber said: 'Opening up civil marriage to same sex couples would be a welcome step forward on the long journey towards achieving equality for LGBT people.
'However, not including religious ceremonies for same sex couples or civil partnerships to heterosexuals who might want this option in the consultation is very short-sighted – and shows we still have a very long way to go before we can talk about real equality and inclusion.'
A similar consultation in Scotland closed on the 9 December, attracting over 70,000 responses, making it the biggest consultation in the history of the Scottish Parliament.
The Scottish government is expected to take a decision on whether to move forward with legislation soon.