The coalition must not listen to the Tory right-wing and throw plans to introduce same-sex marriage into the long grass, shadow equalities minister Yvette Cooper said.
At the Labour party conference in Manchester, Ms Cooper said: "We can build a fairer society, we have done it before.
"We mustn't chuck this into the long grass because of an obsession of the Tory right. People who love each other want to get married. We shouldn't discriminate, we should celebrate.
"It is time to change the law now."
She said religious leaders who backed the coalition's plans must receive political support.
She also attacked critics who claimed to support religious freedom but were opposing the rights of others to hold gay marriages.