Tory MP Tim Loughton has said he believes around 139 Conservative MPs voted against the same sex marriage bill, and possibly as many as 40 of them abstained.
If true, that would mean that a substantial majority of the party did not vote with the Prime Minister.
He told BBC News that he did not see it as a reflection on David Cameron's lack of authority.
Landmark plans to legalise gay marriage got the green light in the Commons, despite a majority of Tories failing to support the Government.
The Prime Minister will read the letter delivered to Number 10, take their views on board, but not change his mind over gay marriage.
Many Conservative MPs just do not understand the move when the tax measure is in the Coalition Agreement.