Gay marriage opposed by Welsh ministers David Jones and Stephen Crabb
Welsh Secretary David Jones will vote against plans to legalise gay marriage in Wales and England.
His fellow Conservative and Wales Office deputy Stephen Crabb will also oppose the move.
Prime Minister David Cameron faces criticism from some Tories for supporting the idea, with Monmouth MP David Davies calling it "barking mad".
Mr Davies said the party would lose loyal activists if it pressed ahead with the policy.
Mr Jones, the MP for Clwyd West, declined to give interviews on the UK government's same sex marriage plans as "this bears no relation to his role as secretary of state for Wales".
Mr Crabb, the Preseli Pembrokeshire MP, fears the proposals will not protect places of worship from a legal challenge should they refuse to carry out ceremonies.
At the weekend, Mr Davies said the idea was "barking mad".
He risked causing controversy by saying most parents "would prefer their children not to be gay, knowing most parents want grandchildren if nothing else".
The UK government will set out its plans soon after a consultation on measures to allow homosexual couples to marry.
Some senior Tory MPs and peers have launched a campaign group backing same sex marriage.
The leader of the Conservatives in the assembly Andrew RT Davies also added his support on Twitter, saying: "The best thing to happen in my life was to meet and marry my wife, it cannot be right to deny two people in love the same feeling".
However, more than 100 Tory MPs are thought to be against legislation, which is expected early next year and on which Mr Cameron has promised a free vote.
The prime minister's official spokesman said: "People have strong views on this issue. The prime minister has strong views as well, and he thinks gay people should not be excluded from marriage.
"We will come forward with our proposals in the next few days. The prime minister's made clear that it will be a free vote for members of parliament."
Under the proposals, churches and other venues will be allowed to "opt in" to holding civil marriage ceremonies.
Mr Cameron has promised that no institution will be forced to marry gay people on their premises if they are opposed to it.