Faith minister Sayeeda Warsi, who attends cabinet, is the latest figure to raise concerns over the policy.
Eight Labour MPs are on record as opposing equal marriage, which Ed Miliband will offer a free vote on.
The party decided to hold a free vote after the government agreed to allow ceremonies in religious buildings.
Is it right to accept something you want from someone who you know gives it with the most cynical of motives, asks Alex Andreou.
The Prime Minister could promise to meet his pledge to introduce a married couples' tax allowance in return for support over the issue.
Conservative MPs criticise PM after he announces that religious organisations will be able to host same-sex weddings.
Gay marriage is right and we must support it if we want to win, Chancellor tells the Tories.
The right are outraged, the left think he's a flip-flopper.
The repeal of Sunday trading laws and the introduction of gay marriage could trigger a backlash.