Supporters of equal marriage have organised a rally in favour of the bill for England and Wales, which will take place on Monday, the same day the bill goes to the House of Lords for committee stage.
Some supporters will begin to rally at 3.30pm, but the majority are expected to arrive between 6pm and 8pm. The meeting point is the statue of George V at Old Palace Yard, London.
Advocates of the rally encouraged supporters to arrive with rainbow and pink jack flags.
Human rights campaigner Peter Tatchell said: “It is important to have a visible presence for equal rights, to counter protests by anti-gay Christian fundamentalists. They want us to remain second class citizens, banned by law from marrying the person we love. In contrast to their intolerance, our rally affirms love and equality for everyone.”
Mr Tatchell said: “This rally for equal marriage is supported by a broad coalition of LGBT activists – and our straight allies – plus supporters of all political parties and none.
“The religious and political opponents of same-sex marriage are an increasingly small and shrill minority who are out of touch with the tolerant, liberal-minded majority. Their stand against marriage equality fuels homophobia and gives comfort to bigots everywhere.
“They say they’re not homophobic but a person who opposes gay equality is homophobic in the same way that a person who opposes black equality is racist.”
He went on to say that equal marriage was important in terms of moves towards equality.
“The legislation seeks to ensure equal marriage rights for all. In a democratic society, everyone should be equal before the law.
“Regardless of whether people agree with homosexuality or matrimony, the ban on same-sex marriage is homophobic discrimination and should be repealed.”
Mr Tatchell went on to say that those unable to attend the rally in person on Monday should use the Out4Marriage site LobbyALord tor encourage peers to support the bill. he said it was important to discourage peers from introducing amendments which could potentially wreck the bill.
Equal marriage critic Lord Dear has proposed another, similar amendment to the Marriage (Same Sex Couples Bill), protecting those who believe marriage is “the union of one man and one woman for life to the exclusion of all others.”
The Marriage (Same Sex Couples) Bill comes back in committee the week commencing 17 June. It will have its report stage on 8 July and third reading on 15 July.
Ministers are hoping that the bill will have Royal Assent before summer recess, at the end of July.